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SSCHSC43170 P0025973

Senior ScienceHSC CourseStage 6

Information systems

Incorporating October 2002

AMENDMENTS

AcknowledgmentsThis publication is copyright Learning Materials Production, Open Training and Education Network –Distance Education, NSW Department of Education and Training, however it may contain material fromother sources which is not owned by Learning Materials Production. Learning Materials Productionwould like to acknowledge the following people and organisations whose material has been used.

• Senior Science Stage 6 Syllabus, Board of Studies, NSW, Amended November 2002

• OTEN (1993) Physics for Electrical and Electronic Engineers

• Spaargaren, S. M. R. Western Australian Women in Science. Sue Spaargaren.< http://www.swimwithdragons.com.au/cgi- bin/cgiwrap/dragons/allegro.pl?wis_search.Sue+Spaargaren > (accessed 28 November 2000).

To complete this module you will need to accessaudio recordings either by:• using the audiocassette: Information systems or• using the internet to access the Informationsystems audio files at www.lmpc.edu.au/science,go to Senior Science, go to Information systems,go to Info systems audio.

All reasonable efforts have been made to obtain copyright permissions. All claims will be settled ingood faith.

Writer: Shelly Hudson

Revised: Richard Alliband

Editors: Julie Haeusler

Illustrator: Thomas Brown

Consultants: Dr Richard Morante (LMP)

Fran Phillipson, Helen Walsh and Colin McKay (Dubbo School of Distance

Education)

Merelyn Devine (Camden Haven DEC)

Anne Migheli (Walgett DEC)

Nella Sharp (Balranald DEC)

Sue Benson (Southern Cross DEC)

Di Skelton (Karabar DEC)

Maria Gavranic (Sydney Secondary DEC)

Yvonne Kinch (OLP)

Jenny Glen (OTEN)

Copyright in this material is reserved to the Crown in the right of the State of New South Wales.Reproduction or transmittal in whole, or in part, other than in accordance with provisions of theCopyright Act, is prohibited without the written authority of Learning Materials Production.

© Learning Materials Production, Open Training and Education Network – Distance Education,NSW Department of Education and Training, 2000. Revised January 2003. 51 Wentworth Rd.Strathfield NSW 2135.

Introduction i

Contents

Module overview ........................................................................ ii

Resources............................................................................................ iii

Icons .................................................................................................... iv

Glossary................................................................................................v

Part 1: Get the message? ...................................................1–34

Part 2: Waves waves waves ...............................................1–30

Part 3: More waves .............................................................1–23

Part 4: Messages from space..............................................1–26

Part 5: Information through impulse ....................................1–20

Part 6: Fibre optics ..............................................................1–34

Student evaluation of module

ii Information systems

Module overview

Welcome to the Information systems module for the HSC component ofthe Senior Science course.

This module explains how mobile phones, radios, telephones, televisions,satellites and satellite dishes work.

You will understand how energy is transformed so that information canbe transmitted from one place to another. Many information systems relyon digital transmissions of light, radio waves or microwaves usingelectricity.

The importance of the electromagnetic spectrum for informationtransmission is addressed as is the difference between AM, FM andmicrowave communication.

You will appreciate the purposes of different satellite orbits and identifythe type of satellites used for live telecast.

Studying how a fax machine works will enable you to better understandhow information can be transmitted in the form of electrical impulses.

Finally you will explore the properties of optical fibres using light andappreciate how they transmit information in telecommunications usinginfra–red radiation.

Even if you are a technophobe, you should enjoy Information systemsand appreciate the advances in technology that now allow us tocommunicate across the globe.

Introduction iii

Resources

You will need the following equipment to carry out activities andexperiments during the module. In most cases, you should have most ofthe items listed around your home.

Part 1 Part 5

• Information systems audiotapeor access to the internet audiofiles

• scissors

• Information systems audiotapeor access to the internet audiofiles

Part 2

• coloured pencils

• glue

Part 3

• household items with barcodes

• string instrument or a rubberband

• portable radio receiver withAM and FM

Part 6

• torch• hammer

• sticky tape

• dark tea towel or hand towel

• two nails of differentthicknesses

Part 4

• toothpicks

• round piece of fruit

• small object such as a raisin orball of blutack

• small amount of blutack orplasticine

iv Information systems

Icons

The following icons are used within this module. The meaning of each iswritten beside it:

The hand icon means there is an activity for you to do. It may bean experiment or you may make something.

The talk icon guides you to discuss a topic with others.

There are exercises at the end of each part for you to completeand send to your teacher.

The headphone icon asks you to complete an activity whilelistening to an audiotape.

The safety icon points out that care needs to be taken whencarrying out a task.

There are suggested answers for the following questions at theend of each part.

This icon suggests you watch a video.

Introduction v

Glossary

The following glossary provides the scientific meaning for many of theterm used in this module, Information systems.

The HSC examiner will expect you to understand the meaning of everyscientific term used. If you find a term that you do not understand, thenlook it up in a scientific dictionary or ask your teacher for assistance.

aerial device for transmitting and/or receivingradio waves

amplitude modulated(AM)

the height of a carrier radio wave ismodified to carry broadcast information;AM radio waves

analog information not coded as ons or offs orzeros and ones

antenna metal wire which detects radio waves

bandwidth the range of frequencies over which anelectromagnetic wave is transmitted

bar code series of black and white lines containingcode information representing themanufacturing country, the manufacturerand the item code

boosting using electricity to enhance a signal forbetter volume and clarity

cathode ray tube vacuum sealed space where a beam ofelectrons is fired at a screen coated withphosphor

cladding in terms of optical fibres; the materialcoating the optical fibre which is lessoptically dense than the core of the opticalfibre

code a collection of symbols or words used forcommunication

coder transforms information into a specificcode

communication system information transfer system

compact disc (CD) thin reflective metallic disc with tiny bitscontaining information for computersand/or stereos such as computer programsor music

compact disc player device for changing compact discinformation into sound

vi Information systems

compression part of a sound wave where the particlesof matter are closest together

constellation (in terms of satellites) a constellation is aseries of satellites which together providedata cover of particular parts of the Earth

crest the highest point of a wave equal to thedensest part of a sound wave compression

critical angle the incident angle at which a beam of lightwill travel along the edge of an opticallydenser medium

decoder transforms coded information into anotherform

demodulator removes the carrier wave from the radiosignal

diaphragm vibrating membrane in microphone orspeaker

digital on and off signals or zero and oneimpulses which carry information

digitised information transferred as a series of onsor offs or zeros and ones

downlink electromagnetic waves transmitted from asatellite to Earth; this transmission may beat a different frequency than the uplink

electromagnetic spectrum(EMS)

electromagnetic waves arranged in orderof increasing energy/increasingfrequency/decreasing wavelength

electromagnetic waves energy carrying transverse waves that arepart of the electromagnetic spectrum thatdoes not require matter to carry the energy

electronic using electricity usually passing throughsolid state components

electrons negatively charged particles; the flow ofelectrons is electricity

elliptical orbit orbit around a central body like the Earththat is closer on one side than the other

email computer based communication usingtelecommunication lines

encryption conversion of easily understoodinformation into symbols so that theinformation is protected and cannot beunderstood by others

Introduction vii

fax (facsimile) machine optically scans information on sheets ofpaper, converting them to digital messagesfor decoding and printing by another faxmachine

fibre optics passing of light through fibre by internalreflection either to transmit light or imagesin medical technology or to communicatein information transfer systems

footprint (in terms of satellites) the area of the Eartha satellite is calibrated to cover forreceiving or transmitting information

frequency the number of waves to pass a point in onesecond

frequency modulated (FM) the frequency of a carrier radio wave ismodified to carry broadcast information

geostationary satellite satellite held in a fixed position in orbitabove the Earth

graded optical fibre optical fibres which are more opticallydense towards the centre and less opticallydense towards the edge of the fibre

hertz (Hz) measurement of frequency; the number ofwaves to pass a point in one second

high Earth orbit geostationary satellites are placed in highEarth orbit 36 000 km above the Earth’ssurface

impulse short burst of energy

incident angle the angle between the normal and theentering light beam

information (transfer) system way of transferring information(meaningful data) from place to place thatuses energy

infra–red waves of the electromagnetic spectrumwith wavelengths ranging from 700 nm to1 mm

Internet worldwide computer networks linkedthrough telecommunication lines andelectromagnetic waves

ionosphere ionised region of the atmosphereextending to about 1000 km above theEarth's surface able to reflect radio waves

kinetic energy movement energy

land connected telephones telephones connected by landlines

viii Information systems

landline wires or cables used as communicationlinks running above or below ground

larynx voice box containing vocal cords

line of sight unimpeded view between two points suchas a transmitter and receiver

longitudinal waves that compress particles of matter,transferring energy in the same directionas the wave movement

low Earth orbit satellite orbit about 1000 km or less fromEarth

magnetic strip strip on credit cards, key cards and traveltickets containing magnetically aligneddigital information

mechanical waves waves that require a medium fortransmission

medium Earth orbit satellite orbit about 10 000 km from Earth

megahertz millions of hertz

micrometre one millionth of a metre

microwaves part of the electromagnetic spectrum from1 mm to 30 cm in wavelength

mobile phone telephone using microwave transmissionsfor communication between transmittingtowers and mobile telephones

modem abbreviation for moulator–demodulator;device that changes digital signals fromcomputer to analog signals that travelthrough copper wires; also changes analogsignals to digital so they can enter acomputer

modulation adjustment of an electromagnetic wave sothat it carries information

multimode optic fibre optic fibre, the thickness of a strand ofhair through which thousands of differentdigital transmissions may be sent

nanometre one billionth of a metre

non–electronic without the use of electricity

non–verbal without the use of words (spoken orwritten or signed)

normal (in terms of optics) perpendicular to thesurface of the interface between twomediums

Introduction ix

optical/optically involving light energy

optical fibres a strand of material (commonly glassfibre) through which light can travel

orbit an object rotating around another object inspace due to the gravitational pull of theobject with greater mass

order of magnitude measurement of size that uses powers often; two quantities of the same order ofmagnitude have different but similar sizes

photodiode light sensitive diode that produces anelectrical output on exposure to light

polarising (with regards to electromagnetic waves)limiting the plane of the electromagneticwave by eliminating waves in other planes

polyurethane (in terms of fibre optics) a waterproofcoating of an optical fibre

radio (receiver) device which tunes into specific AM andFM radio waves for informationtransmission

radio frequency amplifier boosts selected radio frequencies

radio telescope large dish–shaped object to reflect radiowaves to a central receiver; moveable toreceive waves from specific co–ordinatesin space

random access memory(RAM)

where information is temporarily heldelectrically in a computer’s memory

rarefaction part of a wave where the particles ofmatter are furthest apart

receiving dish dish–shaped object that collects thenreflects electromagnetic waves to a centralpoint for collection

refractive index measure of ability of a material to bendlight; the higher the refractive index themore bending of light occurs and the morelikely it is that total internal reflectionoccurs

satellite object held in orbit around a body such asa planet due to gravity

satellite dish reflects electromagnetic waves to areceiver

short waves (SW) AM radio waves of short wavelength andhigh frequency that are reflected by theionosphere and Earth and so used foroverseas broadcasts

x Information systems

silicone (in terms of fibre optics) a flexible layersurrounding an optical fibre and claddingfor protection

small–diameter core optical fibre with a diameter small enoughto fit only one light impulse at any onetime

sound system plays music from compact discs, tapes orthe radio

technophobe person with fear or dislike of moderntechnology

telecommunications any communication involving the use ofconnecting lines or electromagnetic wavesover long distance

television (receiver) cathode ray tube and screen attached to anaerial for radio wave reception; picturesappear on the screen due to the cycling ofan electron beam across the screen

total internal reflection reflection of light off the sides of a densermedium back inside the denser medium

transmitting tower tall tower which sends radio waves ormicrowaves for communication purposes

transverse the direction of energy movement is atright angles to the wave travel direction

trough the lowest point of a wave equal to thezone of lowest pressure in a sound wave

tuner electrical circuit device that selectsspecific radio wave frequencies

uplink electromagnetic waves transmitted to asatellite from Earth

vacuum space containing no particles of matter

verbal using words (spoken or written or sign) asa code between sender and receiver

video conferencing teleconferencing using real–time videoimages over a monitor

visible light part of the electromagnetic spectrumranging from 700 to 400 nm.

wavelength the distance from crest to crest or troughto trough on a wave

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Information systems

Part 1: Get the message?


AMENDMENTS

Senior Science Stage 6 HSC Course

Lifestyle chemistry

Medical technology–bionics

Information systems

• Get the message?

• Waves waves waves

• More waves

• Messages from space

• Information through impulse

• Fibre optics

Option

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Part 1: Get the message? 1

Contents

Introduction ............................................................................... 2

Sending messages.................................................................... 4

Energy...................................................................................................5

Information transfer ................................................................... 7

Telecommunications ............................................................................7

Mobile phones .....................................................................................8

Television............................................................................................10

Compact disc players.........................................................................11

Sound system speakers.....................................................................14

Radios.................................................................................................15

Information systems and society ............................................. 16

Advantages of information systems......................................... 18

Summary................................................................................. 20

Appendix ................................................................................. 23

Suggested answers................................................................. 25

Exercises–Part 1 ..................................................................... 31

2 Information systems

Introduction

In Part 1, you will be given opportunities to learn about the energytransformations in various information systems, which are responsiblefor information transfer. You will be presented with information transferprocesses in mobile phones, telephones, faxes, televisions, soundsystems, CD players and radios and asked to establish a timeline of thedevelopment of these communication systems.

In Part 1, you will be given opportunities to learn to:

• outline the basic pattern of information transfer process as

– code common to both parties

– message

– transmission of coded message

– decoder

• identify a range of information systems used daily

• classify information systems as

– verbal and non–verbal

– short distance and long distance

– electronic and non–electronic

• recall phenomena and events where different forms of energy areused

• identify the transformation of energy at each stage of informationtransfer in one of the following devices

– land connected telephones

– mobile phones

– television

– radios

– Compact Disc players

• discuss the advantages of using a range of information systems.

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In Part 1, you will be given opportunities to:

• gather and process first–hand and secondary information on thebasic pattern of the information transfer process in one of thefollowing systems:

– land connected telephones

– mobile phones

– television

– radios

– Compact Disk players

to outline features that the systems have in common and useavailable evidence to discuss the applications of these systems

• gather and process information from secondary sources to develop atimeline of communication systems introduced to society and use theavailable evidence to analyse the impact these systems have had onsociety and predict possible future directions in communicationtechnologies.

Extracts from Senior Science Stage 6 Syllabus © Board of Studies NSW,November 2002. The most up–to–date version is to be found athttp://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html


Sending messages

Have you ever wondered how land connected telephones and mobilephones work? Do you know how televisions, radios and compact discplayers work?

All of the above technologies have a basic pattern of informationtransfer:

• a code (common both to sender and receiver)

• a message being sent

• transmission of the coded message

• decoding of the message at the receiving end.

If you have heard someone speak in a language you did not understand,you could not receive the message because you did not have the code(knowledge of the language) for decoding.

1 a) Remove the Appendix from the back of this part. Cut out theshaded boxes. You should be left with an A4 sheet of paper withholes in it. This is a code.

b) Place the Appendix over the top of this page (the page you arecurrently reading). The holes in the page should reveal specificwords on this page when the edges are lined up.

c) Write the words below that are revealed by the holes. What is themessage?

_________________________________________________

_________________________________________________

Check your answer before moving on.

Well done. You just decoded a message.

2 What four things are essential for the successful transfer ofinformation?

______________________________________________________

______________________________________________________

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3 Many communication systems (information transfer systems) areused on a daily basis around the world. Seven of these arementioned on the previous page. List these information transfersystems below with any others with which you are familiar.

_____________________________________________________

_____________________________________________________

_____________________________________________________

Check your answers.

The above information transfer systems all use some form of energy.The following section looks at the different forms of energy and theenergy transformations involved in each information transfer system.

Turn to Exercise 1.1 at the back of this part to classify various informationtransfer systems.

Energy

You should remember that energy cannot be created or destroyed, justchanged from one form of energy to another, but do you remember thedifferent forms of energy?

1 Match the forms of energy below with the type of energy involved byusing a line.

Form of energy Type of energy

chemical energy released as traveling vibrations

potential movement energy

kinetic energy carried as waves at the speed of light

heat energy carried by moving electrons

light energy stored in chemicals

sound energy from light source

electromagnetic energy that can be released later

electrical energy from the Sun

solar energy from differences in temperature

nuclear energy released from converting mass intoenergy during fission or fusion

Check your answers before moving on.


2 Knowing that energy can only be changed from one form of energyto another form of energy (like the ones on the previous page), youshould be able to write down the energies before and after each ofthe following scenarios. The first two have been done for you as aguide.

Scenario Energy transformation

sound system playing music electrical sound

car using fuel chemical kinetic

electric light is on ____________ ____________

battery use in a walkman ____________ ____________

boiling an electric kettle ____________ ____________

plants using the sun’s light ____________ ____________

heating food in microwave ____________ ____________

microwave using electricity ____________ ____________

storing the sun’s energy inbatteries

____________ ____________

3 Write three more scenarios and their energy transformations below.

______________________________________________________

______________________________________________________

______________________________________________________

Check your answers.

The transfer of information in information systems may not be as simpleas changing one form of energy into another. Some information systemsmay change one form of energy into several types of energy or changeenergy into different forms of energy and back again.

The following section explains the transformation of energy at each stageof the information transfer process in various information systems.

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Information transfer

Telecommunications

The Information transfer section of the Information systems audiotapecontains information on the information transfer process used intelecommunications. Telecommunications involves telephones, mobilephones, fax communications, paging systems and more.

Listen to the telephone section of the Information systems audiotape or thetelephone internet audio file (at www.lmpc.edu.au/science , go to SeniorScience, go to Information systems, go to info systems audio) to gatherinformation to complete the following activities on telecommunications.

Land connected telephones

hookswitch

to telephone lines

speaker

microphone

Write the information on the following page in the appropriate places on thediagram above using the telephone section of the audiotape/internet audiofiles. Note that electrical impulses are bursts of electrical energy.


• electrical impulses entering telephone

• microphone transforms sound energy into kinetic energy of adiaphragm then electrical energy

• speaker transforms electrical impulses into kinetic energy of adiaphragm then sound energy

• electrical impulses are sent to phone line

• electrical impulses are converted into light energy or electromagneticenergy for long distance transmission.

Check your answers.

Mobile phones

Use the mobile phones section of the audiotape/internet audio files to followthe energy changes in the following diagram then answer the questions onmobile phones over the page.

sound vibrationsproduced in thelarynx – mechanicalenergy

electrical signalconverted tomicrowave

microwaveconverted to anelectrical signalat the cell tower

sound energyconverted toelectrical energy

sound waves convertedto mechanical energy asvibrations of the ear drum

microwave isconverted to anelectrical signaland then tosound waves

electrical signal converted toa microwave at the cell tower

microwave converted toelectrical energy thensent to switching centre

connectingwire

soundenergy

microwave

electrical orlight impulsessent toanother celltower

Energy transformations involved in mobile phone connections.

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1 What energy is converted into electrical energy from mobile phonebatteries?

_____________________________________________________

2 What is sound energy from your voice converted to inside a mobilephone for transmission from the phone to a cell tower?

_____________________________________________________

_____________________________________________________

3 A cell tower boosts a radio wave signal using ___________ energy.

_____________________________________________________

4 After the message is boosted at a cell tower, describe two differentways the message may be sent to the receiving mobile phone.

_____________________________________________________

_____________________________________________________

_____________________________________________________

5 Explain why digital mobile networks are considered to be animprovement on analog networks.

_____________________________________________________

_____________________________________________________

Check your answers.


Television

Use the television section of the Information systems audiotape/internet audiofiles to answer the following questions on how televisions work.

electron beam movesin lines across thescreen 60 times asecond to create apicture

television screen

cord attaches to an antennatelevision isattached toelectricity

cathode ray tube

A television consists of a cathode ray tube with a phosphor coated screen.

a) transmitting tower

__________________________________________________

__________________________________________________

b) receiving antenna

__________________________________________________

__________________________________________________

c) cathode ray tube (picture tube)

__________________________________________________

__________________________________________________

d) screen

__________________________________________________

__________________________________________________

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2 Explain how a single signal can cause an entire picture to appear onthe screen.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

3 Explain the difference between the picture tube televisions and flatscreen televisions and how the images are formed on the screen.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

Check your answers.

Compact Disc players

Use the compact disks section of the audiotape or internet audio files toanswer the following questions on compact discs.

1 Label the layers in the cross–section of a compact disc below.

pits that make the bumps onthe other side

pits are pressed into thepolycarbonate discrepresenting a digital signal incircular tracks

laser lightdirected thisway

1.2 mm


1 600 nm

500 nm

Laser light hits a bump that equals 1 or a no bump which equals 0.The 1s and 0s are reassembled into numbers and used to reconstructthe original sound (or picture) signal.

another track

one track

spin in the direction of the CD

laser path

Compact disc tracks spiral out from the centre. The laser passes along a trackat a constant speed, allowing for a longer rotational period towards the outeredge of the CD.

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2 The arrows in the diagram below show the direction of energytransformation in CD use. Write one of these forms of energy aslabels above each energy change below:

• electrical energy

• sound energy

• light energy.

• kinetic energy

You may use the above forms of energy more than once.

(from power chord)

(from disc spinning around) (from laser beam)

(reflected light is detected)

(energy conversion in a stereo) (energy conversion in a computer)

Check your answers.


Sound system speakers

Use the stereos section of the audiotape or internet audio files to answer thefollowing questions on sound system speakers.

The following diagram shows how information from audiotapes and CDsmoves through a stereo. The numbers on the diagram represent an energytransformation. Write the appropriate transformations of energy in thespaces provided below the diagram.

N

S

magnet

wire coil

speaker

audiotape compact disc

sound waves

wire goes back totape and CD player

Energy transformations through a sound system speaker.

1 ______________________________________________________

2 ______________________________________________________

3 ______________________________________________________

4 ______________________________________________________

5 ______________________________________________________

Check your answers.

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Radios

Use the radios section of the Information systems audiotape/internet audiofiles to complete the following activities.

1 Label each section of the following diagram of a radio with each ofthese labels:

• speaker

• demodulator

• aerial

• tuner

• radio frequency amplifier.

2 Beneath each of the labels, briefly outline the function of each partof the radio.

radio

Inside a radio.

Check your answers.

Antenna or aerial?

An antenna (plural antennae or antennas) is used to receive informationonly. An aerial can transmit, receive or both transmit and receiveinformation at the same time. Radio and TV stations use an aerial tobroadcast their signals. Radio receivers and TV set receivers receivesignals through aerials that can also be called antennas. A mobile phonereceives and transmits phone calls through an aerial.

Turn to Exercise 1.2 at the back of his part to outline the features variousinformation systems have in common.


Information systems and society

You have been presented with information throughout Part 1 about thetime of development of each information system. The majority of thisinformation is in the Information transfer section of the Informationsystems audiotape or the Part 1 internet audio files.

Each communication system has had an impact on society in a differentway.

• Telephones have allowed long distance communication, allowing thefreedom to move and travel while keeping in touch, reducing postaldemand.

• Telephones allow people to work from home while keeping in touchwith the company.

• Advertising, such as telemarketing, can be carried out over the phonerather than on televisions, in newspapers or on radio.

• Radios allow people to hear up–to–date news as it occurs.

• Radios allow a form of advertising for companies and entertainmentfor society.

• Radios have had a huge impact on the music industry, as the latestmusic is broadcast worldwide.

• Television has allowed people to gain clear information onup–to–date events in the world.

• Television has provided a form of entertainment any household canenjoy.

• Television advertising has proven to be the most effective form ofadvertising for many businesses.

• Fax machines have allowed fast transfer of documents, minimisingthe need for postage, thus impacting on the postal system.

• Fax machines allow information to be transferred at convenienttimes, giving people more freedom.

• Mobile phones allow freedom of movement.

• Mobile phones allow people in trouble to call for help if withinmobile range.

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• CDs can allow music and information from anywhere in the world tobe stored and transferred to your stereo or computer, allowing youaccess to cultures around the world.

• CDs can be placed in a stacker which a network of computers haveaccess to; this allows fast access to information without the repetitivephysical loading of a program.

• Sound systems allow society to appreciate music from around theworld through the use of CDs and tapes.

• Email allows the convenience of keeping in touch with people fromaround the world with print and pictures at a lower cost than viatelephone conversations.

• Emailing has reduced the need for postal services.

• Internet chat rooms allow people to interact from around the worldwho would not have otherwise interacted; this technology isexpanding the social circles of society.

• The Internet has allowed society to gain information on any subjectquickly and easily, reducing the need for physical libraries

• Computer based technologies has allowed the development ofthousands of Internet and computer businesses.

As you can see, communication technologies have had a large impact onsociety and will continue to have an impact on society.

In the future, perhaps students will attend school through their computersfrom home; university students won’t need to physically attend lectures;business people won’t need to go to work; people won’t physically goshopping and so on.

Thirty years ago, there were no computers to access, no Internet to surfand no CDs. You might wonder what communication technologies yourchildren will be using in thirty years time.

Turn to Exercise 1.3 at the back of this part to create a timeline ofcommunication systems development and their impact on society.


Advantages of information systems

There are many advantages of having various information transfersystems available such as mobile phones, fax machines, email, Internetaccess, sound systems, radio and television.

• Information may be transferred at the speed of light from one part ofthe globe to another via satellites for transmission to televisions,radios, computers, telephones and fax machines.

• If one form of information transfer is not successful, other formsmay be used.

• Computer based information may be sent via the Internet andreceived immediately or stored on disc or CD for physical transfer.

• Forms may be received, filled out and returned through faxes fromanywhere in the world.

• News from around the world can reach a wide audience throughtelevision or radio transmissions.

• Sound systems can be used to warn people of potential disasters suchas flood or fire.

• Business conversations can be held over mobile phones in transitrather than at particular sites, allowing for greater mobility.

• CDs can store computer instructions and sound information forworld wide distribution.

• Recent developments in video conferencing allows people fromaround the world to engage in meetings without travelling, thussaving time and money.

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Use the clues below to identify the main advantages of various informationsystems.

1

2

3

of

read

sp

4

5

ofst v

Check your answers.

Turn to Exercise 1.4 at the back of this part to discuss the advantages ofusing a range of information systems.


Summary

Write your own summaries next to each of the following informationsystems.

Information system Summary

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1 Each of the above information systems all have a basic pattern ofinformation transfer. Outline the four steps involved in the successfultransfer of information.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

2 Record the energy transformations involved in the transfer ofinformation in the following technologies.

television

_____________________________________________________

_____________________________________________________

telephone

_____________________________________________________

_____________________________________________________

mobile phone

_____________________________________________________

_____________________________________________________


3 Morse code, using dots and dashes to represent letters, was thebasis of an important information system for about 100 yearsuntil recently. Morse code could be sent through wires usingelectricity or wireless (radio) using electromagnetic waves.

Summarise the features of morse code by placing ticks in this table.The definitions for the column headings are in the glossary.

Code

Ver

bal

No

n–v

erb

al

Sh

ort

dis

tan

ce

Lo

ng

dis

tan

ce

Ele

ctro

nic

No

n–e

lect

ron

ic

Morse code

Check your answers.

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Appendix


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Suggested answers

Sending messages1 You have a code for decoding a message.

2 The four things required for the successful transfer of messages are:a code common to the sender and receiver; a message being sent;transmission of the coded message; and decoding of the message atthe receiving end.

3 Information transfer systems used on a daily basis for messagetransfer are: speech; mobile phones; telephones; fax machines;computer emailing; Internet; television; radio; CD players; andpagers. Other answers are acceptable.

Energy

1 Form of energy Type of energy

chemical

potential

kinetic

heat

light

sound

electromagnetic

electrical

solar

nuclear

energy stored in chemicals

energy that can be released later

movement energy

energy from differences in temperature

energy from light source

energy released as traveling vibrations

energy carried as waves at the speed of light

energy carried by moving electrons

energy from the sun

energy released from converting mass intoenergy during fission or fusion


2 Scenario Energy transformation

sound system playing music electrical sound

car using fuel chemical kinetic

electric light is on electrical light (and/or heat)

battery use in a walkman chemical sound

boiling an electric kettle electrical heat

plants using the Sun’s light solar chemical

heating food in microwave electromagnetic heat

microwave using electricity electrical electromagnetic or heat

storing the Sun’s energy inbatteries

solar chemical

electrical impulsesare sent to

telephone lines

speaker transformselectrical impulsesinto sound energy

microphone transformssound energy intoelectrical energy

electrical impulsesconverted into lightenergy orelectromagneticenergy for longdistance transmissionelectrical impulses

entering telephone

Mobile phones1 Chemical energy is converted to electrical energy using mobile

phone batteries.

2 Sound energy from a voice is converted to kinetic energy of amicrophone diaphragm. The electrical impulses resulting areconverted to electromagnetic energy (microwaves) inside a mobilephone for transmission to a cell tower.

3 A cell tower boosts a radio wave signal using electrical energy.

4 A message may be sent to the receiving mobile phone asmicrowaves from the cell tower or converted to light or electricalenergy for transmission along land connected telephone lines toanother cell tower.

5 The digital mobile network can carry more conversations, moresecurely, than an analog mobile network.

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Television1 a) At the transmitting tower, the television signal is converted to

radio waves (electromagnetic energy) and broadcast.

b) A receiving antenna converts the radio waves to electricalimpulses, sending them to the television.

c) The picture tube converts the electrical impulses to a beam ofelectrons (kinetic energy) which it fires to the television screen.

d) A television screen is coated in blue, green and red phosphorthat glows when struck by a beam of electrons.

2 A single beam of electrons moves in lines across the screen 60 timesin one second. This causes the phosphor at different parts of thescreen to glow different colours in that time. This glowing createsan image on the screen.

3 Instead of the electrical impulse being changed to a beam ofelectrons directed at a screen, the electrical impulses are used tocreate electric fields, which affect the liquid crystals in each pixel.This causes different parts of the screen to glow particular colours,forming an image.

Compact Disc players1

125 nm

polycarbonate plastic

labelacrylic

aluminium

pits that make thebumps on the other side

pits are pressed into thepolycarbonate discrepresenting a digitalsignal in circular tracks

laser lightdirectedthis way

1.2 mm

2 electrical energy(from power chord)

kinetic energy(from disc spinning around)

light energy(from laser beam)

electrical energy(reflected light is detected)

sound energy(energy conversion in a stereo)

light energy(energy conversion in a computer)


Sound system speakers1 Information is magnetically detected on an audiotape and used to

produce electromagnetic impulses.

2 The electromagnetic information is sent as impulses through wires tospeakers.

3 These electrical impulses moving through a wire coil produce achanging magnetic field.

4 The magnet vibrates inside the coil as a result of the changingmagnetic field of the wire coil.

5 The movement of the cone attached to the magnet bumps airparticles, causing sound waves.

Radios

aerialdetects allradio waves

tuner tunesinto aparticularfrequency

radiofrequencyamplifierboosts theradio signal

demodulatorcarrier waveremoved fromradio signal

speakerchanges theelectricalsignal tosound energy

radio

Advantages of information systems1 Saves time.

2 Saves money.

3 Speed of information transfer.

4 Worldwide information transfer.

5 Variety of information access.

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Summary1 The four steps for the successful transfer of information are: a code

the sender and receiver both have; a message being sent;transmission of the coded message; and decoding of the message atthe receiving end.

2 Television: electromagnetic energy (radio waves); electrical energy;kinetic energy (beam of electrons); light energy.

Telephone: sound energy; electrical energy; (possibly light energyand back to electrical energy); sound energy.

Mobile phone: sound energy; kinetic energy, electrical energy;electromagnetic energy; electrical energy; electromagnetic energy;electrical energy; kinetic energy, sound energy.

3

Code

Ver

bal

No

n–v

erb

al

Sh

ort

dis

tan

ce

Lo

ng

dis

tan

ce

Ele

ctro

nic

No

n–e

lect

ron

ic

Morse code


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Exercises - Part 1

Exercises 1.1 to 1.4 Name: _________________________________

Exercise 1.1

Place a tick or cross in the following boxes indicating if the informationsystem is: verbal or non–verbal; used over short or long distances; andelectronic or non–electronic.

For each one, think if the message uses words or not, if the message canbe sent over a long distance or not and if it uses electrical energy or not.

Information system

Ver

bal

No

n–v

erb

al

Sh

ort

dis

tan

ce

Lo

ng

dis

tan

ce

Ele

ctro

nic

No

n–e

lect

ron

ic

mobile phone

telephone

television

Internet

radio

audio CDs

CD–ROMs


Exercise 1.2

Various information transfer systems have many similarities eg. twodifferent information systems can utilise digital information transmissionfor information transfer. Explain the similarities between the followinginformation systems.

1 televisions and radios

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

2 radios and mobile phones

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

3 telephones and mobile phones

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

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Exercise 1.31 Use the Information transfer section of the Information systems

audiotape or the Part 1 internet audio files to create a timeline showingthe introduction of each form of communication technology in the tablebelow.

2 Record one impact each communication system has had on societyon the column indicated.

Timeline of communication systems Impact on society

2000

1980

1960

1940

1920

1900

1880

1860

1840


Exercise 1.4

‘Today, anyone can have access to Internet, email, mobile phones,telephones, fax machines, radio, television and even video conferencing.A person running their own lawn mowing business and a stockbroker,buying and selling shares on the stock market, can both benefit from sucha range of information systems.’

Discuss how the two people mentioned in the above statement couldbenefit from the wide range of information transfer systems available.

Record these advantages of information transfer systems in point form inthe table below.

Lawn mowing businessman Stockbroker

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Information systems

Part 2: Waves waves waves


AMENDMENTS


Lifestyle chemistry


Information systems



• More waves



• Fibre optics

Option

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Part 2: Waves waves waves 1

Contents

Introduction ............................................................................... 2

What is a wave?........................................................................ 3

What is the source of a wave? ............................................................4

Waves carry energy .............................................................................5

Sound waves............................................................................. 8

The electromagnetic spectrum ................................................ 10

EMS and communication...................................................................13

Microwave and radio wave use .........................................................17

Summary................................................................................. 20

Appendix ................................................................................ 23


Exercises–Part 2 ..................................................................... 27


Introduction

This part shows how electromagnetic waves can be modulated(adjusted) to carry information. You will become familiar with parts ofthe electromagnetic spectrum and the frequencies that eachcommunication system uses.

In Part 2 you will be given opportunities to learn to:

• identify the type of waves in the electromagnetic spectrumcurrently used for communication systems as

– visible light

– infra–red

– microwaves

– radio waves, which include:

– TV

– FM radio

– AM radio

• compare the advantages and disadvantages of using microwavesand radio waves in communication technologies

• identify communication technologies that use energies from theelectromagnetic spectrum for communication purposes

• describe the individual properties of visible light, radio waves(AM, FM, TV waves) and microwaves and relate these to their usein communication systems.


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What is a wave?

In a communication device, a signal must be carried by something.If no wires connect two communication devices, the signal must becarried by a wave.

You are probably familiar with the waves you see at the beach.The waves in the ocean, that is the ones that aren’t crashing on thebeach, are the shape of the types of waves you will be investigating.If you were able to look at these waves side–on, you would see they arein the shape of the wave diagram below. This is just a model of awave–not all waves look like the one below.

Standard wave.

• The highest point of a wave is the crest.

• The lowest point of a wave is a trough.

• The distance from crest to crest or trough to trough is onewavelength.

• The number of waves to pass a point (like a lighthouse) in onesecond is called the wave frequency.

1 On the above diagram, label the following:

a) crest

b) trough

c) wavelength


2 Frequency is the number of wavelengths to pass a point in onesecond. The units of frequency are hertz (Hz).

a) If 10 waves pass a point in one second, what is the infrequency?

__________________________________________________

b) If 25 waves pass a point in one second, what is the infrequency?

__________________________________________________

c) If 300 waves pass a point in one second, what is theirfrequency?

__________________________________________________

Check your answers.

You are not required to calculate wave frequencies in this course,however this activity will help you understand wave classificationbased on wave frequencies later in this part.

What is the source of a wave?

So what actually produces a wave? Do you have any ideas?

You probably know that when you throw something into a still body ofwater, like a lake or puddle, that waves are produced. This is due to theinitial disturbance of the water particles, or the initial vibration.

Imagine you have set up the apparatus in the following diagram.A mass is attached to a hanging spring and a pen is attached to themass. If you pulled on the mass then let it go, the mass would bob upand down. The pen will mark out a vertical straight line on the paper asthe mass is in motion.

vibr

atio

ndi

rect

ion

straight line

paper is stationary Masson the end of a spring in motion.

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Now imagine the paper is moving at a constant speed past the pen as themass is bobbing up and down at a constant rate. The pen will mark outthe following wave.

vibr

atio

ndi

rect

ion

trace left by pencil is a sine wave shape

paper moving at constant speed

Mass on the end of a spring in motion. A pencil attached to the mass ismarking out a wave as the paper moves past the pencil at a constant rate.

You should notice that:

• the mass is the vibrating object

• the mass moves up and down (not forward and back)

• the wave produced is at right angles to the motion of the mass

• the vibration causes a wave form.

Waves are caused by a vibrating object or particle.

Waves carry energy

If you have ever been dumped by a wave at the beach, you would havefelt the energy of the wave. Even small waves carry energy from oneplace to another.

Different types of waves carry different types of energy and thereforedifferent types of information. For this reason, waves are classifiedaccording to their properties.

There are two main groups of waves. They are electromagnetic wavesand mechanical waves. The characteristics of each type of wave areoutlined in the chart on the following page.


Waves

electromagnetic mechanical

do not require mediumfor transmission

do require mediumfor transmission

all transverse

alternatingelectric andmagnetic fieldsoperatingperpendicularlyto the directionof wave travel

transverse

particles vibrateperpendicularlyto the directionof the wavepropagation

longitudinal

particles vibratein the samedirection aswavepropagation

Different wave types can be classified according to the energy they compriseor the source of the vibration (or disturbance) producing the wave.

1 Which waves do not require a medium (such as a solid, liquid or gas)for transmission?

_____________________________________________________

2 Which types of wave transfers energy perpendicular to an electric fieldor particle movement?

_____________________________________________________

3 Which wave type is produced by particles vibrating in the samedirection as the flow of energy?

_____________________________________________________

4 Which wave type requires a medium (such as a solid, liquid or gas) forwave transmission?

_____________________________________________________


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A vacuum is a space that contains no particles of matter. This means itis entirely empty of solids, liquids and gas. Outer space is a naturalexample of a vacuum as it contains no matter.

5 Can electromagnetic waves travel through a vacuum? Explainwhy or why not.

_____________________________________________________

_____________________________________________________

6 Can mechanical waves travel through a vacuum? Explain why orwhy not.

_____________________________________________________

_____________________________________________________

Check your answers.

Mechanical waves can only deliver information over short distancesdue to the nature of the waves. Sound waves are an example ofmechanical waves, which will be addressed later.

Many communication systems use electromagnetic waves forinformation delivery. These can transfer information quickly and overenormous distances.

Turn to Exercise 2.1 at the back of this part to practice classifying waves.


Sound waves

Turn to the classification of waves chart on page 6. You are about toperform an investigation of mechanical longitudinal waves (these onthe right of the chart).

Sound waves are mechanical longitudinal waves. What this means isthat air particles must bump into each other in order for sound to travel.

Sounds in air travel like the compressions in this slinky spring.

compression

compressionrarefaction

rarefaction

The springs compress and rarefact as the wave pulse moves along the spring.

The areas where the spring is compressed is called a compression.Where the spring has greater space between the springs, it is called ararefaction.

In transverse waves, the wavelength is usually measured from crest tocrest. Longitudinal wavelengths are measured from compression tocompression or rarefaction to rarefaction.

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The air particles below show what longitudinal waves look like in airclose up. Notice the compressions and rarefactions in the sound wave.

wavelength

Air particles compress together as sound waves move through air.

Air particles move in the same direction as the sound energy.Without air particles, sound energy has no medium to be transferred to,therefore sound energy cannot travel.


The electromagnetic spectrum

Do you know what the electromagnetic spectrum is?The electromagnetic spectrum (EMS) is responsible for sun burn,X–rays, everything you see, the heating of food, the music you hear onthe radio, the shows you watch on television and much more.

So what is the electromagnetic spectrum?

The electromagnetic spectrum is a continuum of electromagneticwaves, which are arranged in order of frequency and wavelength.

If that sounds too technical, the following diagram should help as itdemonstrates the various electromagnetic waves of the electromagneticspectrum.

0.01 nm 1 nm 0.1 mm 0.01 mm 1 cm 1 m 1 km 103 km

gammarays

x-rays ultraviolet infra-redmicrowaves

0.4–0.7mm

light TV radioradio waves electrical

power

Wavelength

The electromagnetic spectrum is arranged in order of increasing wavelength.

Adapted from OTEN, Physics for Electrical and Electronic Engineers.

Did you notice the units ‘nm’, and ‘mm’?

These units indicate nanometres (10–9 m) and micrometres (10–6 m).It may be useful to think of the different wavelengths in theelectromagnetic spectrum in the following ways.

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Use the diagram on the previous page to answer the following questions.

1 Highlight or underline which of the following has the shorterwavelength.

a) Gamma rays or television radio waves.

b) Infra–red waves or X–rays.

c) Ultraviolet waves or visible light.

d) Microwaves or infra–red waves.

All electromagnetic waves travel at the same speed which is the speedof light. If a wave has a small wavelength, more waves are able to passa point in one second than a longer wavelength. Keep this in mind asyou answer the following questions.

2 Highlight which of the following are likely to have a higherfrequency? (This means the waves are smaller and therefore morewaves are likely to pass a point in one second.)

a) Microwaves or television radio waves.

b) Infra–red waves or gamma rays.

c) Ultraviolet waves or infra–red waves.

d) X–rays or visible light.

Check your answers.

Remember–electromagnetic waves do not need a medium to betransmitted through, however, particular solids, liquids and gases canabsorb particular electromagnetic wavelengths, stopping theirtransmission.

The following page displays diagrammatic information on the relative sizesof different wave types and instructions for eight activities.

You will need coloured pencils to carry out the eight activities indicated inthe diagram.


Gamma rayswith 0.01 nm

wavelengths can fit 100million wavelengths into amillimetre. Imagine that!

These waves are so small thatthey can affect the genesinside cells. This is why

gamma rays are sodangerous.

Loca

tega

mm

ara

yson

the

electro

magnetic spectrumon

page10

andcolour

ityellow.

Locateradiowav

eson

the

elec

trom

agne

tic

spectrum on page 10 and colour it dark

green

.

The

rad

io w

aves

you

rte

levi

sion

rec

eive

s ar

e ab

out

one

met

re in

leng

th.

Locatetelevisionwavesonth

eel

ectr

omag

net

icsp

ectru

m

on page 10 and colour it green.

Micr

owav

es a

re o

ne

cent

imet

re in

leng

th.

Micr

owav

e ov

ens a

nd m

obile

phon

es b

oth

prod

uce

micr

owav

es.

Locatem

icrowavesontheelectromagnetic

spec

trum

onpa

ge10

and

colour it blue.

Onehundred infrared

waves can fit into amillimetre. You are familiar

with viewing these waves inthermography from the MedicalTechnology-Bionics module. If youhave seen the movies Hollow Man

or Predator, you have seenevidence of infrared waves.Your body is even emitting

infrared radiation as youread this! Locate

infra-red

waves

ontheelectromagneticspectru

m

onpa

ge10

and

colo

urit

re

d.

All the waves you see have

different wavelengths

however generally around one

thousand waves can fit into

a millim

etre

Locate light rays

onthe

electromagnetic

spectrumandleaveitblankto

re

pres

entw

hite

light

.

10 00 wavelengths of

ultraviolet (UV

) light can fitinto one m

illimetre. T

hiselectrom

agnetic wave is

responsible for sunburn.

Loca

te ultraviolet rays on the

electromagnetic

spectrumonpage10andcolouritpurp

le.

One million x-ray

wavelengths fit into a

millim

etre. These waves are

so small that they pass right

through your body.

Loca

tex-

ra

ys on the electromagnetic spectrumon

page10

andcolouritorange.

Sizematters!

The ra

dio w

aves

your

radio

tune

s int

o ar

e ar

ound

100

m

to 1

km in

leng

th!

By now you probably have a good idea that different wavelengths andfrequencies in the electromagnetic spectrum are used for differentcommunication systems.

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EMS and communication

Visible light and infra–red waves

Remember–if one wave passed a point in one second, it would have afrequency of one hertz. If one thousand waves pass a point in onesecond, it would have a frequency of one kilohertz (kHz).

Visible light has a wavelength of 700 to 400 nm.

Infra–red waves have a wavelength of 700 nm to 1 mm.

Visible electromagnetic waves are the colours of the rainbow.Together, all the colours make up white light. Visible light is used toscan pages in fax machines. Visible light waves and infra–red lightwaves are used to transmit digital information at the speed of lightthrough optical fibre telephone lines. (Optical fibres will be furtherdiscussed in Part 6 of this module.)

Fax machines, telephones and computer based communicationsystems all rely on information transmission through telephone lines.These communication systems use the visible light and infra–redsections of the electromagnetic spectrum for communication throughoptic fibres.

Bar codes are scanned using visible light. You may have noticed thered light that is projected onto purchase items at the checkout. This isvisible light used to scan the bar code.

Microwaves

Microwaves are a type of radio wave with a wavelength from 1 mm to30 cm wavelengths. The type of radio waves mobile phones utilise forinformation transmission are microwaves at 824 to 849 megahertz(MHz). This means 824 to 849 million cycles per second or 824 000 to849 000 kHz. Land–based telephone systems also use microwavetowers to transmit information over long distances to the nextmicrowave tower, rather than lay hundreds of kilometres of cables.

Microwaves are used in satellite communication using variousfrequencies.


Radio waves

Radio waves have wavelengths ranging between 30 cm and 1 km.The following information outlines the uses of various wavelengths incommunication.

AM radio waves

AM radio waves are transmitted at 335 kHz to 1.7 MHz (1700 kHz).These waves carry information on amplitude modulated (AM) waves.

A standard carrier wave, using the frequency allocated to the AM radiostation, is combined with the speech wave from the radio announcer ormusic wave from the radio station. The amplitude of the carrier wave ismodified by the speech or music wave from the radio station.The carrier wave is removed from the radio wave inside a radio receiverto select only the speech or music frequencies from the radio station.

AM modulated carrier

Notice the amplitude or the height of the wave is modified (modulated)in the above diagram.

Two–way radios use AM radio waves in much the same way.

FM radio waves

FM radio transmissions occur at frequencies of 88 up to 108 MHz(88 000 kHz to 108 000 kHz). The waves carry information on afrequency modulated (FM) wave.

A carrier wave’s frequency is altered with the addition of speech ormusic from the radio station. Instead of modifying the amplitude orsize of the carrier wave, it alters the frequency of the wavetransmission. This means the number of waves to pass a point in onesecond varies as shown by the following diagram.

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FM modulated carrier

Notice the number of wavelengths to pass a point varies according tothe signal.

FM radio stations use FM radio waves for communication.

Television

Television broadcasting stations transmit their television programsusing at least two FM signals. One signal carries the information forthe television picture and the other carries sound information.Colour broadcasting uses one FM signal for each phosphor colour on atelevision screen, plus an FM sound signal. Sound accompanying atelevision broadcast, is transmitted at 5 MHz above the frequency of thetelevision signal.

Television channels numbers 2–6 transmit at the radio wave frequenciesof 54 MHz (54 000 kHz) to 88 MHz (88 000 kHz) using an FM signal.

Aerial length

Aerial length is about the same order of magnitude as the wavelengthof the electromagnetic waves it is designed to transmit or receive.

The aerial in a mobile phone that receives and transmits microwaves isonly centimetres in length. The metal wire or metal parts in anaerial/antenna for an FM radio receiver or TV set are closer to a metrein length. AM radio receivers have many turns of metal wire that canbe hundreds of metres in length in their aerial/antenna. Similarlytransmitting aerials for AM radio are much longer than for FM stations.

Frequency

The table on the following page shows the parts of the electromagneticspectrum which are used for communication purposes.

1 Record the frequencies in the frequency column on the electromagneticchart on the following page for each communication system from thetext on pages 13–15.*

2 Cut out the pictures in the Appendix and glue them in theCommunication systems column in the chart on the following page.


Wave typeWave frequency

visible light

infra-red

microwave

FM radio waves

TV radio waves

AM radio waves

Frequency Communication systemusing wave

Check your answers.

Turn to Exercise 2.2 at the back of this part to identify the types of waves inthe electromagnetic spectrum used in communication.

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Microwave and radio wave use

Microwaves are a part of the spectrum of radio waves. When peoplerefer to radio waves, they are generally referring to the usual AM andFM radio waves used in radio station and television stationtransmissions. Microwaves have a smaller wavelength and a higherfrequency than the general radio waves. It is these properties that makemicrowaves more or less useful than general radio waves.

Microwaves

There is little difference between frequency modulated (FM) radiowaves and the frequency modulated microwaves used to send signalsfrom mobile phones. The only difference is the frequency bandwidth.Microwave towers can be seen in many parts of inland Australia, onhills and high buildings in country towns. These microwavetransmission towers have replaced the need to connect distant parts ofAustralia by landlines.

The benefits of microwave use in communication are as follows:

• Microwaves are on a different bandwidth of frequency to radiowaves on the electromagnetic spectrum. Crowding of the radiowave bandwidths is a problem.

• Microwaves do not spread out very much so most of the energymakes it to the next receiver dish from the transmitter. This resultsin a signal with the potential range of up to 100 km. Such a systemis important to send information over long distances from tower totower on telephone networks, removing the need for cables.

• It is possible to send a large number of signals at once, because therange of frequencies in the microwave transmission range is large.

• Because microwaves have a shorter wavelength, microwaves havea higher frequency. This means that more information can betransmitted through microwaves in the same amount of time thanradio waves, which have a lower frequency.

• Microwaves can also be received and retransmitted by satellites,expanding the receiving and transmitting area for microwavecommunication.

• Higher frequency waves such as microwaves need less electricalpower for transmission than lower frequency waves such as radiowaves.


Disadvantages of microwave use in communication are as follows:

• Microwaves travel in straight lines and therefore require a line ofsight connection from one antenna to the next. Because of this, amobile network needs a huge number of antennae. Transmittingand receiving aerials used in remote areas for telephonetransmissions without cables need to be built up to 90 m tall forline of sight access to towers 50 to 80 km away.

• Because microwaves travel in straight lines, microwave signalsmay be blocked by hills and mountains. This could be the reasonfor mobile phone connections dropping out whilst in transit.

• Microwaves heat food by water molecules within the foodabsorbing the waves. This fact explains microwave transmissiondifficulties during rain and high humidity as water molecules in theair tend to absorb the microwaves.

• Microwave transmission over the ocean is less successful thantransmission over land as water tends to absorb some of the energy.

• Cell antennas are usually mounted very high on cell towers to haveline of site access over a ten kilometre square area. Interruptions toline of site transmission by hills and buildings can disruptmicrowave–based conversations.

• Microwave signals must be relatively strong for informationtransfer to occur. The microwave signal is strongest at the celltower, losing its strength as it radiates in all directions from thetower. Towards the outskirts of a cell area, mobile phoneconnections tend to break up in clarity or drop out of range. This isbecause the microwave signal is not strong enough to betransformed into electrical impulses by the mobile phone aerial.

Radio waves

Radio waves are beneficial in communication systems for the followingreasons:

• Some radio waves can be transmitted into space and reflected offsatellites. Radio waves are therefore useful for reaching longdistances.

• AM radio waves, unlike FM radio waves and microwaves, do notrequire line of sight access for successful transmission. AM radiowaves can be reflected off objects such as hills, the Earth’s surfaceand layers of the atmosphere. This allows AM radio wavetransmission to distant and remote places without the use ofsatellites.

• AM radio waves of high frequency called short waves (SW) cantravel further at night. Atmospheric layers alter their altitude with

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night–fall, allowing radio waves to be reflected over longerdistances. This is often the reason why at night you can tune intoradio channels broadcast from overseas that cannot be detectedduring the day.

The disadvantages of radio wave use in communication technologiesare as follows:

• Radio waves can be absorbed by water, oxygen and carbon dioxidein the atmosphere, reducing signal intensity.

• Radio waves can be affected by static produced by passing cars,overhead power lines and lightning.

• Low frequency waves such as radio waves need more electricalpower for transmission than higher frequency waves such asmicrowaves.

• Heavy rainfall can absorb radio waves, affecting their transmission.

• Radio wave transmission over the ocean is less successful thantransmission over land as water tends to absorb some of the energy.

• AM radio waves are more affected by atmospheric conditions andfrequency ‘noise’ than FM radio waves and microwaves. Thisresults in static upon reception.

• Because radio waves can be reflected off objects such as land andatmospheric layers, the same signal can arrive at a receiver atslightly different times. This can leave a ghosting effect ontelevisions and an echo sound on radios.

Turn to Exercise 2.3 at the back of this part to compare the use of radiowaves and microwaves in communication.


Summary

1 Write three multiple choice questions and their answers based on theinformation in this part. Make the questions as challenging as youwould expect in an exam.

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2 Write two short answer questions and their answers based on theinformation in this part. Room for questions is also available onthe following page.

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3 Write one long answer question with its answer based on theinformation in this part.

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MACRO MICROSYMBOLICparticles

energyinteractions

H2O

MACRO MICROSYMBOLICobserveinferunderstand

formulasequations

calculations

particlesenergy

interactions

observeinferunderstand

formulasequations

calculations

OH

H

OH

HOH

H

OH

H

Appendix

AMradio

optic fibre

FMradio


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Suggested answers

What is a wave?

1 wavelength crest

trough

2 a) The wave frequency is 10 Hz.

b) The wave frequency is 25 Hz.

c) The wave frequency is 300 Hz.

Waves carry energy1 Electromagnetic waves do not require a medium for transmission.

2 Transverse waves transfer energy perpendicular to an electric fieldor particle movement.

3 Longitudinal waves vibrate particles in the same direction as theflow of energy.

4 Mechanical waves require a medium for wave transmission.

5 Electromagnetic waves can travel through a vacuum because theydo not require a medium for transmission.

6 Mechanical waves cannot travel through a vacuum because theyrequire a medium for transmission.


The electromagnetic spectrum1 a) Gamma rays have a shorter wavelength than television radio

waves.

b) X–rays have a shorter wavelength than infra–red waves.

c) Ultraviolet waves have a shorter wavelength than visible light.

d) Infra–red waves have a shorter wavelength than microwaves.

2 a) Microwaves have a higher frequency than television radiowaves.

b) Gamma rays have a higher frequency than infra–red waves.

c) Ultraviolet waves have a higher frequency than infra–redwaves.

d) X–rays have a higher frequency than visible light.

Electromagnetic waves and communication

Wave typeWave frequency

visible light

infra-red

microwave

FM radio waves

TV radio waves

AM radio waves

824–849megahertz

88–108megahertz

54–88megahertz

535 kilohertz–1.7 megahertz

AMradio

television

FMradio

mobilephone

Frequency Communication systemusing wave

optic fibre

4 millionmegahertz

8 millionmegahertz

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Exercises - Part 2


Exercise 2.1

Identify the following waves as one of the following wave types:

• electromagnetic transverse wave

• mechanical transverse wave

• mechanical longitudinal wave.

You may need to refer to page 6 to help you with your answer.

Wave Wave classification

microwave travelling through space

wave travelling in the ocean

sound travelling through air


Exercise 2.21 Use the scale on the following page to mark the frequency of the

electromagnetic spectrum of following wave types:

• microwaves

• infra–red

• visible light

• radio waves used to broadcast

• TV

• AM

• FM .

2 Next to each wave type, record which of the followingcommunication systems uses one of the listed frequency rangesduring communication:

• optic fibre infra red information transfer

• television

• AM radio

• mobile phone

• optic fibre visible light information transfer

• FM radio.

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Frequency Wave type Communicationtechnology using thiswave frequency

8 000 000 000kHz

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4 000 000 000kHz

___________________ _____________________

849 000 kHz

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824 000 kHz

108 000 kHz

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88 000 kHz

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54 000 kHz

1 700 kHz

___________________ _____________________

535 kHz


Exercise 2.3

Many of the advantages and disadvantages of using radio waves andmicrowaves are identical. Use the information on microwaves andradio waves for communication to identify the benefits anddisadvantages of microwave and radio wave use in communicationsystems.

Wav

e Advantages Disadvantages

mic

row

aves

radi

o w

aves

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Information systems

Part 3: More waves


AMENDMENTS


Lifestyle chemistry


Information systems

• Get the message


• More waves



• Fibre optics

Option

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Part 3: More waves 1

Contents

Introduction ............................................................................... 2

Properties of the EMS ............................................................... 3

Speed of travel .....................................................................................3

Ability to travel in a straight line ...........................................................4

Ability to be reflected............................................................................5

Wave modulation....................................................................... 7

AM and FM radio waves ......................................................................8

Summary................................................................................. 11


Exercises–Part 3 ..................................................................... 17


Introduction

Part 3 looks in closer detail at the properties of electromagnetic wavesand their uses in information systems. You will perform an investigationto observe communication with AM and FM waves.

In this part you will be given opportunities to learn to:

• identify that where information systems cannot be physically linkedthe information may be transmitted in wave form through theatmosphere or space

• identify the properties of energy from the electromagnetic spectrumthat make it useful in communication technologies including its

– speed of travel

– ability to travel in a straight line

– ability to be reflected

In this part you will be given the opportunities to:

• perform a first–hand investigation to observe ways in which wavescan be modified to carry different types of information

• plan, choose equipment or resources for, and perform a first–handinvestigation to compare the quality of reception of AM and FMradio waves.


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Properties of the EMS

Three useful properties of energy from the electromagnetic spectrum are:

• the speed of travel

• ability of waves to travel in a straight line

• ability of waves to be reflected.

Speed of travel

All waves in the electromagnetic spectrum travel at the same speed–thespeed of light. Light travels at 300 000 km per second. Allelectromagnetic waves travel at this speed.

It might be difficult to comprehend just how quickly these waves travel.An electromagnetic wave can travel around the Earth more than six timesin one second. That’s pretty fast!

Use a pencil to draw a cartoon demonstrating electromagnetic wavestravelling at high speed. Be as inventive as you like!


You outlined the communication technologies which use part of theelectromagnetic spectrum for communication purposes in Part 2.

Outline why the speed at which waves travel is important in communicationtechnologies such as in telecommunications.

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Check your answer.

Ability to travel in a straight line

Electromagnetic waves travel in straight lines unless acted on by ainfluencing field. This is an important aspect of electromagnetic wavesas they can be directed to a specific receiving dish, allowing line ofsight transmissions in communications eg. microwave transmissionsfrom telecommunications towers.

This property of electromagnetic waves also allows waves detected fromspace to be used to pinpoint the location of the transmitting signal.This allows scientists to locate and map stars and galaxies, controlastronomical instruments on satellites and track the passage of spacecraftthrough space.

Draw a cartoon demonstrating electromagnetic waves travelling in straightlines.

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Explain why electromagnetic waves travelling in straight lines is animportant property for use in communication technologies.

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Ability to be reflected

Electromagnetic waves can be reflected off surfaces. This is a veryimportant property of electromagnetic waves. Reflection allows:

• waves to be transmitted across the globe using the reflectiveproperties of the ionosphere and the Earth’s surface

• a weak signal to be collected by a receiving dish.

The diagram below shows a transmitting tower sending electromagneticwaves. The wave travels through the atmosphere in a straight line and isreflected by the ionosphere. From here, the wave bounces back to Earthwhere it can then be reflected off the surface of the Earth and so on.

1 Label the following on the diagram below based on the informationfrom the previous paragraph:

• transmitter

• reflected wave

• ionosphere

Earth

An electromagnetic wave is reflected off the ionosphere, allowing the wave to betransmitted to parts of the globe with no line of sight.


Waves can be collected and reflected to a single point by a satellite dish.The following diagram demonstrates how the curvature of the dishallows the focusing of the reflected waves to the receiver.

Pay TV delivered without cables relies on information transfer in thisway. Telecommunications towers also rely on the principles of wavereflection at the satellite dish. Communication with space shuttles andreceiving information from space probes in outer space relies on thesame principles–on a much larger scale.

2 Label the satellite dish and the reflected waves on the followingdiagram.

A satellite receiving dish utilising the reflective properties of waves to focus thewaves to a receiver.

3 Explain the importance of the reflective capabilities ofelectromagnetic waves in their use in communication technologiessuch as receiving dishes.

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Check your answers.

Although the speed of electromagnetic waves, their ability to travel instraight lines and their reflective capabilities remain constant, waves canbe modified to carry different types of information.

Turn to Exercise 3.1 at the back of this Part to outline the properties ofwaves from the electromagnetic spectrum that make those electromagneticwaves useful in communication technologies.

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Wave modulation

You might not realise that a change in the pitch of a sound or a change insound volume is a result of wave modulation. The different colours yousee are a result of wave modulation. Particular colour wavelengths areremoved when white light reflects from objects resulting in you seeing aparticular colour. Infra–red waves are modified by differences in heat.Radio waves are amplitude modulated for AM radio, or frequencymodulated for FM radio.

In each instance, wave modulation (modification) allows differentinformation to be transmitted.

A wave can be modulated in two main ways:

• amplitude modulation (the height of the waves)

• frequency modulation (the number of waves which pass a point inone second)

Imagine modulating the simple wave below.

1 Redraw the above wave with its amplitude (the height of the wave)modulated.


2 Redraw the original wave with a modulated frequency (the numberof waves to pass a point).

Turn to Exercise 3.2 at the back of this part to modulate waves to carrydifferent information.

AM and FM radio waves

AM and FM radio waves are the result of modulated carrier waves.AM waves are an amplitude modulated carrier wave and FM waves are afrequency modulated carrier wave.

Part 2 discussed the differences between AM radio waves and FM radiowaves. You may need to use this information to answer the followingquestion.

1 Draw an AM wave below.

2 Draw an FM wave below.

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3 Outline the main difference between AM and FM radio waves.

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The atmosphere often contains ‘noise’ that can interfere with anelectromagnetic wave such as a radio wave. Have you ever noticed aradio signal sound scratchy as you drive under power lines or yourtelevision picture becoming fuzzy when an electrical appliance in thehouse is running? This is because an electromagnetic field is interferingwith the radio wave, which in turn, causes the signal to become fuzzy.

AM radio waves are easily affected by ‘noise’. The following diagramdemonstrates how this noise combines with an AM wave, causing afuzzy reception.

equals modified AM signal – this is alteration that producesthe static you hear

plus noise signal

amplitude modulated signal

AM signal plus noise.

FM radio waves rely on altering the frequencies of the wave rather thanthe wave amplitude. It is much harder to change the frequency of a wavethrough noise, therefore FM reception is much clearer than AMreception.


4 Which type of radio waves are more likely to be affected by static?Briefly explain your choice.

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FM radio channels require a large bandwidth of the electromagneticspectrum. The range of frequencies required to transmit the signal islarge. This limits the number of FM channels available.

AM radio requires a much smaller bandwidth of frequency fortransmission so the number of potential AM channels transmitted ismuch larger.

Again, you may need to use the information on AM and FM waves inPart 2 to answer the following questions.

5 What frequency bands do AM radio stations use?

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6 What frequency bands do FM radio stations use?

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7 Which radio signal uses higher frequencies, AM or FM?

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Check your answers.

Waves from the electromagnetic spectrum are used in ways you may nothave thought of.

Turn to Exercise 3.3 at the back of this part to plan and carry out aninvestigation comparing AM and FM radio communication.

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Summary

1 Satellite dishes rely on which property of electromagnetic waves tofocus the waves onto a receiver?

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2 You can have a conversation on a mobile phone with someone 5000 kmaway with no time delay in the conversation due to which property ofelectromagnetic waves?

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Circle the correct answer for questions 3–4.

3 Changing the pitch of a sound is the result of changing the wave:

frequency; amplitude; plane of vibration.

4 Changing the volume of a sound is the result of changing the wave’s:

frequency; amplitude; plane of vibration.

5 What are the two main ways of modulating radio waves?

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6 Explain the difference between AM and FM radio waves.

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7 Explain why AM waves are more affected by static than FM waves.

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Suggested answers

Speed of travelTelecommunications benefit from the speed of information transfer asphone calls and satellite communications from across the globe, such asthe transmission of live television programs from other countries, areachieved at a fast rate without time delay.

Ability to travel in a straight lineElectromagnetic waves can be focused to a point for collection at adistance due to the fact that the waves travel in straight lines.The location of stars, galaxies and space shuttles can also be pin pointeddue to this property of electromagnetic waves.

Ability to be reflected

1

Earthtransmitter

reflected wave

ionosphere (atmosphere layer)

2

reflected waves

satellite dish


3 The reflective capabilities of electromagnetic waves allows waves tobe reflected to a receiver. This is important in communication fromspace, pay TV using satellite dish technology andtelecommunications. Electromagnetic waves being reflected offatmospheric layers allows transmission further around the globewithout the use of repeater stations eg. radio wave transmissions.

Wave modulation

1

2

AM and FM radio waves

1

2

3 The amplitude of a carrier wave is modified to carry an AM radiosignal. The frequency of the carrier wave is modified to carry an FMsignal.

4 AM radio waves are more likely to be affected by static than FMwaves because the amplitude of a radio wave is more easily affectedby ‘noise’ than the frequency of a wave.

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5 AM radio stations use frequency bands from 335 kHz to 1.7 MHz.

6 FM radio stations use frequency bands from 88 to 108 MHz.

7 FM radio uses higher frequencies than AM radio.

Summary1 Satellite dishes rely on the reflective properties of electromagnetic

waves to focus the waves to a receiver.

2 You can have a conversation on a mobile phone with someone5000 km away with no time delay due to the speed ofelectromagnetic waves.

3 Changing the pitch or tone of a sound is the result of changing thewave frequency.

4 Changing the volume of a sound is the result of changing the wave’samplitude.

5 Amplitude modulation (AM) and frequency modulation (FM).

6 AM radio waves carry information in a carrier wave with a modifiedamplitude. FM radio waves carry information on a carrier wave witha modified frequency.

7 AM waves are more affected by static than FM waves because waveamplitude is more easily affected by ‘noise’ than wave frequency.


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Exercises - Part 3


Exercise 3.1

Identify three properties of waves from the electromagnetic spectrumthat are useful in communication technologies.

For each, outline the importance of the property in terms of informationtransmission where the information systems cannot be physically linked.

i) _____________________________________________________

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ii) _____________________________________________________

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iii) _____________________________________________________

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Exercise 3.2 Observing ways in which waves can bemodulated to carry information

Amplitude

The first way you will modify a wave is by changing the amplitude of awave. Believe it or not, when your parents complain about the volume ofyour music, they are actually complaining about the amplitude of thewaves coming from the speakers.

If you have a guitar, violin or any other string instrument, you can use itfor the following activity. If not, you can achieve the same outcome witha tightly pulled rubber band between two fingers or two objects kept thesame distance apart.

1 Gently pluck one string on a musical instrument or a tightly pulledrubber band. You should hear a sound and see the string or rubberband vibrating. Notice the volume of the note and the size of thestring or rubber band vibrations.

Record your observations below.

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2 Now pluck the string or rubber band harder. What difference isthere in the sound? Look at the vibration of the string–how is itdifferent to plucking the string or rubber band gently?

Record your observations below.

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3 The amplitude of the string or rubber band is altered by how hardyou pluck the string or rubber band. Explain how this relates to thedifference in sound that is heard.

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Frequency

You can alter the frequency of a wave using the same string instrumentor rubber band.

4 If using a string instrument, pluck one string with your fingerholding down the string in one place. Repeat this with your finger indifferent places on the string as shown below.

If you are using a rubber band, alter the tension on the rubber bandby loosening it or pulling it tighter then pluck it. Repeat this with adifferent tension on the rubber band.

What do you notice about the sound as you pluck the string or rubberband?

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5 Holding the string in different places puts more or less tension on thestring as does altering the tension of the rubber band. Altering thetension alters how quickly the string is able to vibrate. Use yourobservations to fill in the missing words below with the wordshigher or lower.

a) The more tension on the string, the _________________ the

frequency and the _________________ the pitch.

b) The less tension on the string, the _________________ the

frequency and the _________________ the pitch.

6 Sound waves clearly carry information. Describe how thatinformation carried by sound waves changes when

a) the amplitude increases ________________________________

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b) the frequency increases ________________________________

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Exercise 3.3

You must plan, choose equipment and resources for and perform aninvestigation to compare the quality of reception using AM and FMradio waves.

You have access to AM and FM radio waves through your radio receiver.If you live somewhere where you do not receive AM and FM radiosignals, you may plan your investigation now and complete it whenpassing through towns on your next trip using the car radio.

You must carry out the following tasks in your investigation.

• Record the radio stations you are investigating and their frequency[remember 900 2LM really stands for 900 kilohertz (kHz) and96.1 FM really stands for 96.1 megahertz (MHz)].

• Record the bandwidth you can pick the signal up on with some staticeg. 900 2LM could be received over 895–905 kHz.

• Record the quality of AM reception compared to FM reception.

• Draw conclusions as to why a radio signal can be received over abandwidth range, linking it to the information on page 10.

• Draw conclusions on the clarity of signal received on AM and FMbands and relate these to AM and FM radio wave transmissions.

Here are some suggestions for your investigation.

• Compare the reception of AM and FM radio signals when in an areaof interference such as under power lines.

• Try several different AM and FM radio stations.

• Try to chose AM and FM signals that are strong.

• Predict the results you expect in a column in your results table suchas the bandwidth you expect to receive a particular radio station overand the clarity of reception.

• Assess the accuracy of your predictions in your discussion.

• Comment on anything that went wrong in your discussion such as aweak signal.

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Record your investigation using the following scaffold.

Aim

What are you investigating?

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Method

What steps are involved in carrying out the experiment? Try to addressall the points above.

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Results

How will you present your results? Will you make any predictions?If so, clearly state they are predictions as opposed to results. Make sureyour results are clear and easy to understand.

Discussion

Assess the accuracy of any predictions and give scientific reasons foryour results. Discuss any situational issues such as poor radio receptionand how the experiment could be improved.

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Conclusion

Explain the similarities and differences between AM and FM radiosignals that are supported by your results. Link your results to yourknowledge of AM and FM radio waves from pages 8 to 10.

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Information systems

Part 4: Messages from space


AMENDMENTS


Lifestyle chemistry


Information systems



• More waves



• Fibre optics

Option

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Part 4: Messages from space 1

Contents

Introduction ............................................................................... 2

Geostationary satellites ............................................................. 3

Use of geostationary satellites.............................................................5

Earth–based satellite dishes................................................................7

Satellite orbits.......................................................................... 11

Satellites.................................................................................. 14

Summary................................................................................. 15

Appendix ................................................................................. 17


Exercises–Part 4 ..................................................................... 23


Introduction

Almost everything you ever wanted to know about satellites is addressedin this part. You will learn about: satellite orbits; what satellites are usedfor; various parts of satellites; and the importance of calibrating satellitedishes for optimum reception.

This part deals with geostationary satellites and how they relay andtransmit information.

• explain why the satellite must be at a height where its revolutionperiod is the same as that of the Earth’s period of rotation

• explain why the Earth–based satellite dish must face a fixeddirection if it remains in the same location with respect to thegeostationary satellite.


• gather, process and analyse information from secondary sources toidentify the satellites used for ‘live’ telecasts from other regions ofthe world to Australia and vice versa and to present reasons whycommunication satellites have different aerials and positional orbits.


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Geostationary satellites

1 Collect a round piece of fruit such as an apple, orange or peach.

2 Stick a toothpick (or a small stick) into the piece of fruit.

3 On the other end of the toothpick (or stick), place a small object such asa raisin, jelly bean or a ball of Blutac® .

4 Move the round piece of fruit through a 360° rotation. Notice theposition of the small object on the end of the toothpick through therotation.

5 Draw your apparatus below using arrows to indicate the rotation ofthe fruit, the toothpick and the object on the end of the toothpick.

Keep your model for an experiment later in this part.

You have just demonstrated the action of a geostationary satellite.

You should know that satellites are objects held in orbit around a planetby the planet’s gravitational pull. But what does geostationary mean?

6 What do you think geo means?

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7 Explain the term stationary.

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8 What do you think is meant by the term geostationary satellite?

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Check your answers against the following definition.

Geostationary satellites are held in a fixed position in orbit abovethe Earth.

Geostationary satellites orbit around 36 000 km above the Earth’ssurface. The toothpick in your fruit experiment represented this distance.If you think that the state of New South Wales is almost 2000 km across,then you can appreciate just how far away these satellites are in space.Even at this distance, geostationary satellites are nowhere near the moonwhich is nearly ten times this distance away from the Earth.

For satellites to be held in a fixed position above the Earth, they must be:

• close enough to the Earth to be held in orbit by the Earth’sgravitational pull

• far enough away from the Earth to prevent it from being pulled fromorbit to the Earth by the Earth’s gravitational pull.

This critical height above the Earth is called the high Earth orbit(HEO). All geostationary satellites orbit the Earth in the HEO.

A geostationary satellite must orbit the Earth at the same rate as theEarth rotates–one revolution in a 24 hour period.

Your fruit experiment demonstrated this rule–as the object at the end ofthe toothpick (the geostationary satellite) finished in the same place itbegan after a full rotation. In reality, this is a twenty four hour period ofrotation. If the satellite orbited the Earth any faster or slower than this,the satellite would not be a geostationary satellite as it would not alwaysbe in the same position above the Earth at any one time.

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Answer true (T) or false (F) to the following statements.

1 Geostationary satellites orbit the Earth. T F

2 Geostationary satellites orbit 2000 km above the Earth. T F

3 HEO stands for high Earth orbit. T F

4 Geostationary satellites must orbit the Earth in the HEO. T F

5 Satellites in HEO are pulled to Earth by gravity. T F

6 Satellites in HEO may float off into space. T F

7 A satellite is a man made object in orbit around a planet. T F

8 A geostationary satellite orbits the Earth once in 24 hours. T F

9 Geostationary satellites pass quickly across the sky at night. T F

10 In your experiment, the toothpick represents 36 000 km. T F

11 The large round piece of fruit represents a satellite. T F

12 The small object on the toothpick represents a satellite. T F

Check your answers.

Turn to Exercise 4.1 at the back of this part to locate the orbital area ofgeostationary satellites.

Use of geostationary satellites

You should understand that satellites can be used to transmit or reflectelectromagnetic waves from one part of the world to another.

1 What do you think satellites that remain in a fixed position abovecontinents would be used for? Remember, this is a module aboutInformation systems, so try to relate your answer to the informationtransfer systems you have studied.

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A geostationary satellites is in a fixed position above the Earth’s equator.A geostationary satellite has a constant line of sight access to a specificarea of the Earth. The area of the Earth a geostationary satellite can sendand receive messages from is called a footprint.

The information transmitted to and from geostationary satellites includes:

• live or commercial television programs

• telecommunications

• telephone conversations

• digital information transfer

• broadband internet access

• video conferencing.

Often a single geostationary satellite carries out all the functions aboveat once!

A ground level transmitting station transmits information such as atelevision broadcast from America to a geostationary satellite at aparticular wave frequency. This is called the uplink. The satellite iscapable of receiving, amplifying and retransmitting the electromagneticwave to a target such as Sydney. Alternatively the satellite can receivethe wave, amplify it then change its frequency before sending back toEarth. Either method can be used as a downlink from satellite to Earth.

For a satellite to alter an electromagnetic wave, it needs power.You don’t hear about astronauts changing satellite batteries in spacebecause the big arms you see on satellites are actually covered in solarpanels. The panels absorb energy from the Sun, storing it as chemicalenergy in rechargeable batteries for use during the night section ofthe orbit.

Finish the following sentences based on the above information.

1 Three uses of geostationary satellites are ____________________

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2 An uplink is ___________________________________________

3 A downlink is __________________________________________

4 Satellites have solar panels ________________________________

______________________________________________________

5 A geostationary satellite footprint is ________________________

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Check your answers.

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Have you seen a satellite dish attached to a house? Does your homehave one? The following section explains the link between geostationarysatellites and satellite dishes.

Earth–based satellite dishes

Use the round fruit, toothpick and small object from the model you builtearlier in this part to complete the following activity.

1 The Appendix contains small pictures of satellite dishes. Turn to theAppendix to cut out these five satellite dishes now.

2 Break three toothpicks in half.

3 On the same side of the round fruit that the original toothpick is stickingout of, push the sharper end of five of the broken toothpicks deep intothe fruit, leaving around one centimetre of the toothpick exposed. Thiscan be done anywhere on the fruit, however it must be on the same sideof the fruit as the ‘satellite’.

4 Stick the five satellite dishes to the ends of the five brokentoothpicks with small balls of blutack or plasticine.

5 Manoeuvre each of the five satellite dishes so they are pointingtowards the satellite. Draw your model in the space below.

6 Rotate the piece of fruit through a full rotation (360°).


1 As you rotate the fruit (representing the Earth) through 360°, do thesatellite dishes remain facing the object at the end of the toothpick(which represents the geostationary satellite)? Record yourobservations.

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2 Once Earth–based satellite dishes are aligned to have a line of sightconnection with a geostationary satellite, do they need to be movedto account for the Earth’s rotation? Use your model to explain youranswer.

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Check your answers.

Satellite dish alignment

The diagram below shows how a satellite dish reflects waves from ageostationary satellite to a receiver at a central point. The shape of thedish is critical for the reflected waves to be focused to the receiver.

reflected waves

satellite dish

Electromagnetic waves being reflected and focused to a receiver by a satellitedish.

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The Earth–based satellite dish needs to directly face the satellite toreceive clear reception. A clear reception is dependant on the intensity ofthe waves hitting the dish. A dish must be calibrated at a right angle(90°) to the waves entering the atmosphere for optimum reception. If thedish is at another angle to the satellite, the intensity of the waves reachingthe dish would be reduced, therefore reducing the quality of reception.

waves from satellite

receiver

satellite dish

Electromagnetic waves reflected to a receiver by a satellite dish.

1 Is the above Earth–based satellite dish directly facing the satellite(which is sending the waves)? How do you know this?

_____________________________________________________

_____________________________________________________

2 Is the Earth–based satellite dish above receiving a strong or weaksignal? Explain your answer.

_____________________________________________________

_____________________________________________________

waves from satellite

receiver

satellite dish

Satellite dish reflecting electromagnetic waves to a receiver.


3 Is the satellite dish on the bottom of the previous page facing thesatellite, which is sending the waves? How do you know this?

______________________________________________________

______________________________________________________

4 Is the satellite dish receiving a strong or weak signal? Explain youranswer.

______________________________________________________

______________________________________________________

5 If a satellite was sending a television signal to the satellite dish onthe previous page, explain why you would you expect the program tobe clear or fuzzy.

______________________________________________________

______________________________________________________

______________________________________________________

Check your answers.

Radio telescopes collect radio waves from space the same way satellitedishes do. Radio telescopes are much larger as they need to collectwaves over a larger area to receive a signal from space. Radio telescopesare moveable to receive waves from specific co–ordinates in space.Satellite dishes differ from radio telescopes in that they are much smallerand are designed to remain stationary for uninterrupted contact with aspecific geostationary satellite. Satellite dishes generally receivetelecommunications and television transmissions.

The only problem with geosationary satellites is a quarter of a secondtime delay in information transmission. The distance of a geostationarysatellite above the Earth’s equator is 36 000 km. A wave travels around70 000 km when transmitted to the satellite and back to Earth. It takesaround a quarter of a second for this to occur as electromagnetic wavestravel at 300 000 km per second. If information has to make two satellitejumps, for information to reach the other side of the world, the time delayis slightly longer.

To appreciate the importance of radio telescope dishes facing the directionof the point source of waves, you might like to watch the movie The Dish asan optional activity.

Turn to Exercise 4.2 at the back of this part to draw conclusions on satellitesused for live telecast to other regions of the world.

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Satellite orbits

Have you ever seen a satellite move across the sky at night?These satellites are moving faster than the rotation of the Earth and are inan orbit closer to the Earth. In fact there are several different orbitssatellites can be placed in depending on the use of the satellite.

Label the following on the diagram below.

1 The outer circle is the high Earth orbit (36 000 km from Earth).

2 The next circle in from the high Earth orbit is the medium Earth orbit(10 000 km from Earth).

3 The two egg–shaped orbits are elliptical orbits.

4 The circular orbit closest to the Earth is the low Earth orbit (1000 kmfrom Earth).

Satellite orbits around Earth.

Check your answers.


Over 3500 satellites have been launched into space since the firstsatellite, Sputnik, in 1957. You might be wondering why differentsatellites use different orbits. There are several reasons.

• Geostationary satellites must orbit in high Earth orbit due to thegravitational forces. Because they are stationary with respect to theEarth, uninterrupted television and telecommunication transmissionscan take place but with some time delay.

• Medium Earth orbit satellites are also often used in land imagery,telecommunications and weather forecasting. Telecommunicationsoften need to be transferred from satellite to satellite to maintain aconnection between widely separated ground earth stations.Time delay in information transfer is insignificant at this height.

• Elliptical orbits are similar to the orbit of a comet. This type of orbitallows the satellite to travel closer to Earth, around 800 km abovethe Earth, than the circular low Earth orbit satellites. A series ofsatellites in elliptical orbits transmit television programs to Russianhomes and Canadian homes. These homes cannot be reached bysignals from geostationary satellites which are always above theequator. The elliptical orbit satellites must travel at high speedswhen close to the Earth and are therefore not in range for long, so aseries of satellites with similar orbits must be used.

• Low Earth orbit satellites are most commonly used for highresolution land imagery and mobile telecommunications to and frommobile phones, ships and aeroplanes. These satellites are travellingat high speeds at a number of angles across the globe. One of agroup of around fifteen satellites is ensured to have line of sightaccess to anywhere on the globe at any one time, however thesatellites must be tracked to change transmission from one satelliteto another without loss of the signal. A series of satellites used forthis purpose is called a constellation. Because these satellites are soclose to Earth, there is negligible time delay in informationtransmission. The diagram below demonstrates the movements ofthese low Earth orbit satellites.

A series of Low Earth orbit satellites (constellation) allow for global mobiletelecommunications.

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Imagine you are studying for a test. You are reviewing importantinformation you expect the examiners to include. What do you think theexaminers are likely to test for with regard to satellite orbits?

Examiners are likely to ask you to locate the different orbits, whatsatellites in different orbits are used for and make a prediction such astime delays for satellites in particular orbits.

Use a highlighter to highlight information on the previous page that is likelyto be examined in a test.

The next section deals with the components of satellites themselves.

Turn to Exercise 4.3 at the back of this part to complete a task on satelliteorbits.


Satellites

The satellite below has four main components:

• solar panels

• receiving aerial

• electrical circuitry

• transmitting aerial.

Guess where each of these labels above belong on the satellite below.Hints: a bigger aerial is needed to receive waves from Earth; and the ‘arms’are not aerials.

A typical satellite.

Check your answers.

Uplink information is transmitted from a ground station to the receivingaerial in the form of electromagnetic waves. This information can rangefrom television broadcast or digital fax information to a phoneconversation or digitised Internet information. The wave is then boostedand the frequency of the wave altered by electrical circuits in thesatellite. The downlink wave is then sent to a receiving station by thetransmitting aerial where the wave is then sent to its destination, such asa home telephone.

Turn to Exercise 4.4 at the back of this part to interpret an Earth/satellitediagram.

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Summary

As you complete the following find–a–word, think about the significanceof the words in relation to the information you have learned in this part.

Find the following words in the find–a–word below.

orbittelecommunicationstelevisionlow earth orbitdownlinkright angleconstellation

solar panelsgravityuplinkreceiving aerialtwenty four hoursfrequencyintensity

geostationary satellitehigh earth orbitelectromagnetic waveelliptical orbitsatellite dishtransmitting aerial

G T C T U I O S D E F W A N J K L S R R J O

Q E L E C T R O M A G N E T I C W A V E F H

T C O N S T E L L A T I O N T U G A W C B M

E W C S B N J K O R R U Y K L F R H N E B M

L S T H T R A N S M I T T I N G A E R I A L

E R D A E A A A H Y K J C Z T Y V Z W V A O

C F G G S W T E L E V I S I O N I R M I D W

O H S E G A E I H T K A Q F B M T H U N F E

M G A Y Y R E D O W N L I N K O Y U R G U A

M N T K I I U A H N A H C C B I T I D A I R

U I E L L I P T I C A L O R B I T J S E L T

N O L L O K L I S T A R T O O I L L H R L H

I G L O R L I T M N H T Y E Y O K S E I Y O

C A I I X P N E I N T E N S I T Y A F A R R

A D T U N P K L A F L J J M A T O T F L A B

T W E N T Y F O U R H O U R S T P B K H N I

I G D T I R O S B J L T T U O O E H L N O T

O H I D K V L S S O L A R P A N E L S K R M

N I S H L N V A W D G J Y E D H K L L L B N

S P H V F R E Q U E N C Y C C E R E T I I B

H L G A F M B H I G H E A R T H O R B I T D

C R I G H T A N G L E D G H F R P O F V R E

Check your answers.


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Appendix


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Suggested answers

Geostationary satellites1 Geostationary satellites orbit the Earth. T

2 Geostationary satellites orbit 2000 km above the Earth. F

3 HEO stands for high Earth orbit. T

4 Geostationary satellites must orbit the Earth in the HEO. T

5 Satellites in HEO are pulled to Earth by gravity. F

6 Satellites in HEO may float off into space. F

7 A satellite is a man made object in orbit around a planet. F

8 A geostationary satellite orbits the Earth once in 24 hours. T

9 Geostationary satellites pass quickly across the sky at night. F

10 In your experiment, the toothpick represents 36 000 km. T

11 The large round piece of fruit represents a satellite. F

12 The small object on the toothpick represents a satellite. T

Use of geostationary satellites1 Three uses of geostationary satellites are: live television

transmissions; telephone conversation transmission and internetbroadcasting. Other answers are acceptable.

2 An uplink is the transmission of a wave to a satellite at a particularfrequency.

3 A downlink is the transmission of a wave from satellite to Earth at aparticular frequency.

4 Satellites have solar panels to absorb energy for use in boosting andaltering wave frequencies.

5 A geostationary satellite footprint is the area of the Earth ageostationary satellite can send and receive messages from (line ofsight).


Earth–based satellite dishes1 As the fruit (Earth) rotates through three hundred and sixty degrees,

the satellite dishes remain facing the geostationary satellite becausethe satellite does not move relative to the Earth.

2 Once satellite dishes are aligned to have a line of sight connectionwith a geostationary satellite, they do not need to be moved toaccount for the Earth’s rotation. The model shows that once asatellite dish is calibrated to have a line of sight connection with asatellite, it will maintain that calibration throughout the Earth’srotation.

Satellite dish alignment1 The satellite dish is directly facing the satellite, which is sending the

waves because all the waves hitting the dish are being reflected tothe receiver and the dish is at right angles to the waves.

2 The satellite dish is receiving a strong signal because waves from thesatellite are being reflected from the entire dish to the receiver andthe dish is at right angles to the waves.

3 The satellite dish is not directly facing the satellite because the dishis not at right angles to the waves and waves are not hitting the entiredish.

4 The satellite dish is receiving a weak signal because waves are nothitting the entire dish for reflection to the receiver, cutting down onthe energy received.

5 If a satellite was sending a television signal to this satellite dish theprogram would be fuzzy because the dish is not detecting all thewaves it could, resulting in a weak signal.

Satellite orbits

eliptical orbitslow Earth orbit(1000 km)

Earth

medium Earth orbit(10 000 km)

high Earth orbit(36 000 km)

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Satellites

receiving aerial

transmitting aerial

electrical circuitry

solar panels

Summary

R

E L E C T R O M A G N E T I C W A V E

T C O N S T E L L A T I O N G C

E R E

L T R A N S M I T T I N G A E R I A L

E V V O

C T E L E V I S I O N I I W

O S T N E

M A D O W N L I N K Y G A

M T U A R

U E L L I P T I C A L O R B I T E T

N L L R H

I L I I O

C I N I N T E N S I T Y A R

A T K L B

T W E N T Y F O U R H O U R S I

I D O T

O I S O L A R P A N E L S R

N S B

S H F R E Q U E N C Y I

H I G H E A R T H O R B I T

R I G H T A N G L E


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Exercises - Part 4


Exercise 4.1

The following diagram of a geostationary satellite in orbit above theEarth is missing three labels. Use the information from pages 3 to 5 tocomplete these labels.

km

2 Give two reasons why geostationary satellites must orbit in the highEarth orbit region.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________


Exercise 4.2

The diagram below shows a satellite positioned to send and receivemessages from two countries. It provides for live telecast of televisionprograms, telephone conversations, digital information transfer andvideoconferencing between these two countries.

Satellite with two footprints for live telecast between countries.

1 Explain why the satellite used for live telecast in the above diagramis likely to be a geostationary satellite.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

2 Explain why geostationary satellites are positioned above theequator.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

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Exercise 4.3

Complete the missing information in the table below on satellite orbits.

Orb

ital

fea

ture

s (t

ime

del

ay,

sate

llite

sp

eed

an

d t

rack

ing

)

insi

gnifi

cant

tim

e de

lay;

sate

llite

s tr

ansm

issi

onch

ange

s fr

om s

atel

lite

tosa

telli

te a

s in

divi

dual

sate

llite

s m

ove

out o

f ran

ge

Sat

ellit

e u

se

high

res

olut

ion

land

imag

es;

mob

ile te

leco

mm

unic

atio

nsw

ith m

obile

pho

nes,

shi

psan

d ae

ropl

anes

Orb

ith

eig

ht/

styl

e

10 0

00 k

mab

ove

Ear

th

ellip

tical

pat

h;ca

n tr

avel

with

in80

0 km

of t

heE

arth

Sat

ellit

e o

rbit

high

Ear

th o

rbit


Exercise 4.4

The diagram shows a satellite in use. In the space provided, write aparagraph explaining what is happening in the diagram from theoriginating ground station to the destination ground station. Be sure toidentify the differences between the transmitting and receiving aerials inyour paragraph.

originatinggroundstation

destinationgroundstation

receive aerial and receiver transmit aerial and transmitter

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

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Information systems

Part 5: Information through impulse


AMENDMENTS


Lifestyle chemistry


Information systems



• More waves



• Fibre optics

Option

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Part 5: Information through impulse 1

Contents

Introduction ............................................................................... 2

Coding and decoding information.............................................. 3

Energy transformations ............................................................. 7

Electrical impulses..................................................................... 8

Generating electrical impulses ............................................................9

Summary................................................................................. 12


Exercises–Part 5 ..................................................................... 19


Introduction

Part 5 places information that you have learned through Parts 1–4 incontext. You will identify the energy transfers involved in coding anddecoding information by the digital technologies.


• identify communication technologies that transform one type ofenergy into electrical energy

• describe the transmission of images using digital technologies interms of scanning of the input image along very thin lines

• explain how the coding of the image into a series of zeros and onesallows its transmission and ultimate decoding

In this part you will be given opportunities to:

• gather, process, analyse and present information from secondarysources to identify energy transfers involved in coding and decodinginformation by digital technologies.


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Coding and decoding information

Most modern communication systems transfer information using digitaltechnologies.

Coding converts information into binary coded form which uses thedigits 0 and 1. The digital transmission is by electrical, light orelectromagnetic impulses representing the 0s and 1s. Decoding changesthe 0s and 1s impulses received back to information which can beunderstood by the receiver.

Digitised information is very resistant to interference and noise:

plus noise

digitised signal

equals modified digital signal – but itis still clear whether the value is a oneor a zero

0

1


In this section you will gather, process, analyse and present informationfrom audio tape/internet files. The audio files, and diagrams supplied inthis print material, should help you identify the energy changes involvedin coding and decoding information using digital technologies.

You can become better informed by using the audio files on faxes (anabbreviation for facsimiles), computer–based information systems andemailing and internet.

Faxes (Facsimiles)

Use the faxes section of the Information systems audiotape/internet audiofiles to answer the following questions on fax machines.

Fill in the missing words in the following sentences.

1 Fax information is optically _________________ along very thin

_________________ across the page.

2 A page is broken up into a _________________ consisting of verysmall _________________.

3 The scanner records the number _________________ in the box

when scanning a dark section and a _________________ when

scanning a white section.

4 This light energy information is transformed by a photodiode into

_________________ energy and sent along phone lines.

5 The receiving _________________ machine puts

_________________ in the small grid boxes with ones and leaves

the boxes with zeros _________________.

6 Colour in the following boxes labelled with the number ‘1’ and leavethe boxes with the number ‘0’ blank. Complete the first row first,then move to the next row and so on.

What message is being sent?

0 0 1 0 0 1 0 0 0 0 0 1 1 0 0 0 0 0 0 1 1 1 0 0 0

0 0 1 0 0 1 0 0 0 0 1 0 0 1 0 0 0 0 1 0 0 0 1 0 0

0 0 1 0 0 1 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0

0 0 1 1 1 1 0 0 0 0 0 1 1 0 0 0 0 1 0 0 0 0 0 0 0

0 0 1 0 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0

0 0 1 0 0 1 0 0 0 0 1 0 0 1 0 0 0 0 1 0 0 0 1 0 0

0 0 1 0 0 1 0 0 0 0 0 1 1 0 0 0 0 0 0 1 1 1 0 0 0

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You just decoded a fax message in a similar way to afax.

Check your answers.

Computer–based information systems

When a computer uses the telephone system to communicate withanother computer a modem (abbreviation for modulator/demodulator) isused between the computer and the transmission line. An externalmodem lies outside the computer while an internal modem is insidethe computer.

If you send an email or use the internet you will be using a modem tofacilitate transmission of your data.

Use both the computer–based information systems and emailing andInternet sections of the Information systems audiotape/internet audio filesbefore answering the following questions.

1 In the grid below, colour in the boxes with on written in the box andleave the boxes with off blank. What letter does this code of ons andoffs make?

off off on off off off

off on on on off off




off off on off on off

off off on on off off


Answer true (T) or false (F) to the following questions.

2 Email and Internet information may be sent along phone lineswithout modems.

3 Computer information is stored digitally as a series of zeros andones in the random access memory.

4 Modems send coded digital information as ones and zeros, eachat different frequencies down phone lines.

5 Modems can only send digital information, not receive anddecode information.

6 Computer based information systems uses electrical energy totransfer information.

Check your answers.

____

____

____

____

____

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Energy transformations

Parts 1 and 5 have outlined the energy transformations involved ininformation transfer in various information systems. You should now beable to identify the different energy transfers involved in each type ofinformation system.

Complete the following activity to refresh your memory.

Match the following information systems with the basic energytransformations involved in each by writing one of the followinginformation systems on the blank lines below:

sound system; radio receiver; mobile phone; television receiver;telephone; and facsimile.

sound electrical impulses (and light impulses)

sound

electromagnetic waves electrical impulses

kineticenergy

(beamofelectrons)

lightenergy

electrical or light energy + kinetic energyelectrical im

pulsessound

electromagnetic energy electrical impulsessound

optical energy electrical impulseskinetic energy

(inkgoing

ontopaper)

sound electrical impulses electromagneticwaves

electrical impulses

electromagnetic

waves

electricalimpulsessound


Turn to Exercise 5.1 at the back of this part to identify communicationtechnologies that transform different energies into electrical energy.


Electrical impulses

You should appreciate that a page being faxed is optically scanned and isrecorded as a series of electrical impulses of ones and zeros or ons andoffs, which are transmitted down telephone lines to a receiving faxmachine. The receiving fax machine places ink in the grid where itreceives an on or one signal and leaves blank areas when it receives anoff or zero signal.

1 Explain how a page is broken up for scanning by a fax machine.

_____________________________________________________

_____________________________________________________

_____________________________________________________

2 Given that digital ons and offs or zeros and ones have differentfrequencies and a faxed page is transmitted through phone lines inthis way, explain how a fax machine prints an almost identical copyof the original page with this digital pulse information.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

Check your answers.

Turn to Exercise 5.2 at the back of this part to complete a task on digital faxtransmissions.

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Generating electrical impulses

You are familiar with electrical energy. You know that if you turn on alight, electrical energy is converted to light energy by the light globe.You should also know that electrical energy is essentially converted tosound energy for you to listen to your stereo. Common householdenergy transformations like these convert electrical energy into anotherform of energy. Have you ever thought of changing one form of energyinto electrical energy?

When you use batteries in your camera, walkman or remote control car,you are changing chemical energy from the batteries into electricalenergy. This electrical energy is then used to wind on the film, play yourmusic or move the remote control car’s wheels.

When you use a microphone, sound energy is converted into an electricalsignal. When an aerial receives radio waves, it converts these waves intoan electrical signal. Power stations burn coal to heat water, whichproduces steam. The kinetic energy of the steam turns turbines whichturn generators to produce electricity, thus turning kinetic energy intoelectrical energy. Hydro–electric schemes also use the kinetic energy ofwater to produce electricity. These are all common examples ofchanging one form of energy into electrical energy.

Think about the different forms of energy that are changed into electricalenergy at some stage in different information technologies.

1 Mobile phones and telephones change what form of energy into anelectrical signal?

_____________________________________________________

2 Televisions and radios change what form of energy into electricalsignal?

_____________________________________________________

3 Fax machines and long distance telephone lines (optical fibres) convertwhat form of energy into electrical energy?

_____________________________________________________

Check your answers.

Computer based communication systems change electrical energy intoimpulses of electrical energy representing zeros and ones for emailing andinternet information transfer through telephone lines.


The Electrical impulse section of the Information systems audiotape explainsthe following diagrams and what each experiment is expected to show.Listen to and complete the activities outlined on this section of theaudiotape.

1

cathode ray oscilloscope

microphone

wire

Sound energy converted to electrical impulses.2

voltmeter(multimeter)

battery

wire tapping key open(open circuit)

Tapping key open preventing flow of electricity through the circuit.


battery

wire tapping key closed(closed circuit)

Tapping key closed allowing flow of electricity through the circuit.

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3

microammeter(multimeter)

wire coilmagnet

needle alternatesbetween these two

positions

wire

Magnet moving into and out of a wire coil.

Check your answers.


Summary


Use a mind map approach to surround the following syllabus points withthe relevant information you have learnt throughout this part.

identify communicationtechnologies that transformone type of energy intoelectrical energy

describe the transmissionof images using digitaltechnologies in terms ofscanning of the inputimage along very thin lines

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explain how the codingof the image into aseries of zeros and onesallows its transmissionand ultimate decoding

gather, process, analyseand present informationfrom secondary sourcesto identify energytransfers involved incoding and decodinginformation by digitaltechnologies


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Suggested answers

Faxes (Facsimiles)1 Faxes information is optically scanned along very thin lines across

the page.

2 A page is broken up into a grid consisting of very small boxes.

3 The scanner records the number one in the box when scanning a darksection and a zero when scanning a white section.

4 This light energy information is transformed by a photodiode intoelectrical energy and sent along phone lines.

5 The receiving fax machine puts ink in the small grid boxes with onesand leaves the boxes with zeros blank.

6 0 0 1 0 0 1 0 0 0 0 0 1 1 0 0 0 0 0 0 1 1 1 0 0 0

0 0 1 0 0 1 0 0 0 0 1 0 0 1 0 0 0 0 1 0 0 0 1 0 0

0 0 1 0 0 1 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0

0 0 1 1 1 1 0 0 0 0 0 1 1 0 0 0 0 1 0 0 0 0 0 0 0

0 0 1 0 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0

0 0 1 0 0 1 0 0 0 0 1 0 0 1 0 0 0 0 1 0 0 0 1 0 0

0 0 1 0 0 1 0 0 0 0 0 1 1 0 0 0 0 0 0 1 1 1 0 0 0

Computer based information systems

1on

on

on

on

onononon

on

on

on


2 Email and Internet information may be sent along phone lineswithout modems.

3 Computer information is stored digitally as a series of zeros andones in the random access memory.

4 Modems send coded digital information as ones and zeros, eachat different frequencies down phone lines.

5 Modems can only send digital information, not receive anddecode information.

6 Computer based information systems uses electrical energy totransfer information

F

T

T

F

T

Energy transformations

sound electrical impulses (and light impulses)

sound

electromagnetic waves electrical impulses

kineticenergy

(beamofelectrons)

lightenergy

electrical or light energy + kinetic energyelectrical im

pulsessound

electromagnetic energy electrical impulsessound

optical energy electrical impulseskinetic energy

(inkgoing

ontopaper)

sound electrical impulses electromagneticwaves

electrical impulses

electromagnetic

waves

electricalimpulsessound

mobile phonetelevision

sound systemfacsimiletelephone

radio

receiver

receiver

Electrical impulses1 A page is broken up for scanning by a fax machine into a fine grid.

Light and dark information on the page is recorded in this grid.

2 An on pulse frequency for a particular grid co–ordinate causes a faxmachine to place ink on paper in that grid space. An off impulsefrequency causes the fax machine to leave the grid co–ordinateblank. This process occurs a large number of times to form analmost identical copy of the original page.

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Generating electrical impulses1 Mobile phones and telephones change sound energy into electrical

energy.

2 Televisions and radios change electromagnetic energy into electricalenergy.

3 Fax machines and long distance telephone lines (optical fibres)convert light energy into electrical energy.

1

cathode ray oscilloscope

microphone

wire (carrying electrical impulse)

2


battery

wire tapping keyclosed

(closed circuit)(electrical

impulses carriedin wires)

3

microammeter(multimeter)

wire coil(electricalimpulse)

magnet

needle alternatesbetween these two

positions

wire(electricalimpulse)


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Exercises - Part 5


Exercise 5.1

For four information technologies, record the energy type that istransformed into electrical energy. You may use the information onpage 6 to help you with your answer. A form of energy changed intoelectrical energy for mobile phones has been done for you as a guide.

Information technology Energy type before transforminginto electrical energy

mobile phone sound energy


Exercise 5.21 Explain the energy conversion involved in sending a fax by a fax

machine.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

2 What information is sent through telephone lines to the receiving faxmachine?

______________________________________________________

______________________________________________________

______________________________________________________

3 Explain how the receiving fax machine interprets the informationsent through the telephone line in order to print a copy of the originalfax.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

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Information systems

Part 6: Fibre optics


AMENDMENTS


Lifestyle chemistry


Information systems



• More waves



• Fibre optics

Option

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Part 6: Fibre optics 1

Contents

Introduction ............................................................................... 2

Bending light ............................................................................. 3

Total internal reflection.........................................................................4

Optical fibres ............................................................................. 8

So what is an optical fibre?................................................................10

Copper cables and optical fibres .......................................................14

Australian research in fibre optics ........................................... 17

Appendix ................................................................................. 19

Sue Spaargaren .................................................................................19


Exercises–Part 6 ..................................................................... 27

Bibliography ............................................................................ 33


Introduction

Part 6 outlines the principles of information transmission through opticalfibres. You will learn how light can follow the twist and turns of opticalfibre without escaping and compare the efficiency and carrying capacityof copper cables against optical fibres in telecommunications.


• outline properties of optical fibres as communication carriers

• outline the principle of total internal reflection and relate this to theadvantages of fibre optics over more conventional carriers ofinformation

• outline the differences and relative merits in the use of fibre opticscables and metal cables to transmit and receive information.

In this part you will be given opportunities to:

• perform a first–hand investigation to demonstrate the transmission oflight through an optical fibre

• process and analyse information from secondary sources to compareand contrast copper cables with fibre optic cables in relation to

– carrying capacity

– cost

– rate of information transfer

– security.


Although light can pass through optical fibre and is used in thesenotes and activities about optical fibre, most of the electromagneticradiation used in modern optical fibre communication systems isinfra red radiation with a frequency about half that of red light.

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Bending light

The following activity is best done at night, however you may observethe results in a darkened room during daylight.

Read through the following instructions first to identify the equipmentyou will need to complete the task.

1 Collect a medium to large old glass jar with a lid.

2 Use a hammer and nail to punch two holes in the lid on opposite edgesof the lid. One hole should be small and the other hole should be larger.Try to use a thin and a thicker nail to make clean circular holes.

3 Three quarters fill the jar with water and place the lid on top firmly.

4 Use small pieces of sticky tape to cover the holes on the surface ofthe lid to stop water leakage.

5 Lie the jar on its side on the kitchen sink or on an outside bench.The larger hole in the lid should be closest to the sink or bench.You may need to support the jar to prevent it from rolling. Be awarethat water will be coming out of the large hole in the lid–so set upthe apparatus so it doesn’t make a mess.

6 Turn on a torch and place the torch face at the base of the jar asshown below. Again, you may need to support the torch to preventit from rolling.

torch jar

small holein lid

large holein lid

Torch facing the base of a glass jar.

7 Cover the torch and jar with a dark towel so only the jar’s lid isexposed.

8 Remove the sticky tape covering the holes and observe, using yourobservations to answer the following questions.


1 What do you notice if you place your finger in the stream of water in theplaces shown in the following diagram?

torch water

jar lid

place your finger inthe stream of waterin these three placesglass jar

streamof water

_____________________________________________________

_____________________________________________________

2 Is the light from the torch held completely within the stream of water ordoes the light shine straight through the lid hole as if the jar was empty?

_____________________________________________________

3 Can you suggest why light, which travels in straight lines appears tobend in this experiment?

_____________________________________________________

_____________________________________________________

_____________________________________________________

Check your answers.

The following section explains the phenomenon you just observed.

Total internal reflection

Despite what you witnessed in the previous experiment, light alwaystravels in straight lines. Light is part of the electromagnetic spectrum.Do you remember studying the reflective properties of electromagneticwaves in Part 3? You should recall the diagrams showing radio wavesbouncing off layers in the atmosphere and waves being reflected bysatellite dishes. Light is no exception to this rule of reflection.

You might be baffled as to how light appears to curve in a stream ofwater if it is true that light only travels in straight lines. The answer liesin total internal reflection.

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Each diagram below shows a beam of light travelling from a relativelydense medium such as glass to a less dense medium such as air.The dotted line down the centre is an imaginary line perpendicular to thesurface of the glass called the normal. This line is used to measure theangles of light beams. The angle between the normal and the enteringlight beam is called the incident angle.

1 For each of the diagrams below use a ruler and a pencil to join dots Band C, then draw an arrow on the line indicating the direction of thelight.

a)

less densemediumfor example air

more densemediumfor example glass

norm

al

A

B

C.

b)



norm

al

A

B C.

c)


more densemediumfor exampleglass

norm

al

A

B

.


2 Explain what happens to the beam of light from B to C in diagrama) on the previous page. Indicate if it moves into a more dense orless dense medium and if its angle changes or not.

______________________________________________________

______________________________________________________

3 Look at the angle of the light line between the line A to B and thenormal in diagram a) (the incident angle). Is this angle smaller orlarger than the same angles in the other diagrams?

______________________________________________________

4 Explain what is happening to the light line from B to C in diagramon diagram b) on the previous page. Be sure to identify if it leavesthe denser medium or not.

______________________________________________________

______________________________________________________

5 Does the line B to C have a different angle to the normal than theline A to B in diagram b)?

______________________________________________________

The angle between A and B and the normal in diagram b) is calledthe critical angle. This means the angle at which the beam of lightwill travel along the edge of the denser medium.

6 Is the angle between the light line from A to B and the normal indiagram b) (the incident angle) larger or smaller than diagram a)?

______________________________________________________

7 Explain what is happening to the light line from B to C in diagramc) on the previous page. Indicate which medium it moves into.

______________________________________________________

______________________________________________________

8 The light line from A to B on diagram c) is being reflected backinside the glass. Is the angle between A to B and the normal (theincident angle) greater or smaller than the first two diagrams?

______________________________________________________

9 Look at the angles between A and B and the normal and B and C andthe normal in diagram c). Are these angles the same or different?You may use a protractor to be sure.

______________________________________________________

Check your answers.

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Light travelling from a denser medium to a less dense mediumexceeding the critical angle is totally internally reflected andstays within the denser medium.

All the above statement means is that at whatever angle light travels inthe glass above the critical angle, the light will always be reflected backinside the glass. This is shown in the diagram below.

angles greaterthan thecritical angle

light beam atcritical angle

criticalangle

result of critical angle

total internalreflection

Total internal reflection of light inside a tube of glass. Light at an angle greaterthen the critical angle is totally internally reflected.

Long, thin cylinders of glass called optical fibres use the principles oftotal internal reflection for information transmission.


Optical fibres

The following activity demonstrates how light travels through optical fibres.

1 Join the points A, B, C, D and E on the first optic fibre below.

2 Join the points A, B and C on the second optic fibre below.

3 Join the points A, B, C and D on the third optic fibre below.

air(less dense)

air(less dense)

optic fibre 1(moredense)



A A A

C

E

B

D

B

B

C

C D

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Reconstruct the following sentences.

4 total through Light fibres by reflection. travels optic internal

_____________________________________________________

_____________________________________________________

5 optical angles light walls. reflect off Different fibre of

_____________________________________________________

_____________________________________________________

Check your answers.

Remember the digital information that is sent along telephone lines(as ons and offs or zeros and ones)? Many telephone systems use lightwaves in optical fibres to carry this digital information.

A light wave travelling through an optical fibre can represent the ons andoffs or zeros and ones information. The on or one light signal has adifferent frequency than the off or zero light signal. Your voice isconverted to these digital impulses to travel at the speed of light throughlong distance telephone lines.

Digital fax information, internet information and email information alltravel the same way through optical fibres in telecommunicationsnetworks.

You might be wondering how your voice gets transmitted as light signalsalong optical fibres. Remember–the sound of your voice is just a form ofenergy. This energy is converted to light energy which represents theway you speak. When the light energy reaches its destination, it isconverted back to sound energy. Digital computer based information ischanged to light energy and back again in a similar way.



So what is an optical fibre?

An optical fibre is a strand of material (commonly glass fibre)through which light or infra–red radiation can travel.

The diagram below shows thin strands of plastic optical fibres on the endof a torch.

Optical fibres carrying light from a torch.

As you can imagine, a long thin strand of glass the thickness of a hair isnot very strong. For this reason, optical fibres require cladding.The cladding needs to be of lower refractive index than the strand ofglass to ensure total internal reflection within the glass fibre.

There are three main types of optical fibres used for telecommunications.

Multimode optical fibre

total internal reflectionof several light impulses

within the optic fibre

light enteringcladded optical

fibre

optic fibre

cladding with lowerrefractive indexthan optical fibre

Multimode optical fibre.

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Thousands of different digital transmissions may be sent along amultimode optical fibre. The light impulses are often sent in theinfra–red band of the electromagnetic spectrum. The glass inside thecladding has a consistent refractive index throughout the fibre.

Graded optical fibre

optic fibre has a gradeddensity causing light to travelfaster on the edges of the

fibre than the centre

graded optic fibre

cladding with lowerrefractive index oroptical densitythan optical fibre

Graded optical fibre.

Imagine running 100 metres, but instead of running in a straight line, youzig–zagged across the track to the finish line. Would you have travelledfurther than if you had run in a straight line? Of course you would have.

Light impulses bouncing off the edges of an optical fibre would alsotravel much further than light that barely touched the edges. This causesimpulses to arrive at their destination at slightly different times.

Graded optical fibres have a higher refractive index material towards thecentre of the fibre. The refractive index gradually decreases towards theouter edges of the fibre. This causes light inside the optical fibre toappear to curve, although light is still travelling in a straight line.

The result of graded optical fibres is all the light transmissions,regardless of how many times they are internally reflected, arrive at theirdestination at the same time. This prevents time delays in transmission.Quality of output information is better than for the multimode optic fibre.


Small diameter core

small diameter core optical fibre (3–5 mm)

cladding

Small diameter core.

The glass strand inside this optical fibre is only 3–5 µm (3 –5 x 10–6 m)in diameter and only transmits a single impulse at any one time.Only one light wave can fit inside the inner core at one time. An impulseof light travels through the high refractive index material centre.

Because there is no interference with other waves and the light containedinside the core cannot spread out due to the size of the core, the quality ofthe information transmitted is excellent and does not need to be boostedfor 500 km. Small diameter optical fibres are therefore often used inlong distance cables, however the precision lasers required to beam theimpulses through these fibres and the technology required to aligntheir tiny cores cause them to be more expensive than other opticfibre varieties.

1 What is the difference between a multimode optic fibre and a gradedoptic fibre?

_____________________________________________________

_____________________________________________________

2 Why is an optic fibre strand encased in cladding?

______________________________________________________

______________________________________________________

3 What problem does graded optical fibre attempt to overcome?

______________________________________________________

______________________________________________________

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4 Which type of optical fibre is more effective in long distancetelecommunications and why?

_____________________________________________________

_____________________________________________________

You have identified a glass strand and its cladding however optical fibresare surrounded by several more layers for strength and durability.

5 Label the diagram below with the following:

• the thinnest tube is the glass core and cladding combined;together they form the optical fibre

• the next layer is silicone

• the next layer is the buffer jacket

• the second last layer is the strength layer

• the outside layer is polyurethane

6 Label the above diagram as a single optical fibre.

Check your answers.

Even with the protective layers, optical fibres are quite flexible.Rarely is one optical fibre laid alone in telecommunications. Bundles ofoptical fibres such as the one above are usually encased inside a cable intelecommunications.

Turn to Exercise 6.1 at the back of this part to summarise the properties ofoptical fibres.


Copper cables and optical fibres

Copper cables are still used in telecommunications for local networks.Instead of your voice being changed in to light impulses, it is changedinto electrical impulses at different frequencies for transmission alongcopper cables.

The advantages optical fibres have over copper cables are outlinedbelow.

• Optical fibres carry information at the speed of light, allowing moreinformation transmission in one cable than transmission by electronsin electric signals in copper cables.

• Optical fibres totally internally reflect light impulses, therefore lessenergy is lost and information is more precisely transmitted than incopper cables which can distort signals and lose energy in the formof heat due to electrical resistance in the wire. Optical fibrestherefore allow for greater clarity in information transfer.

• Thin optical fibres made of glass are much lighter than the thickercopper cables needed to carry the same volume of information.Thousands of conversations can be transmitted through a series ofcopper cables with the diameter the size of a tennis ball or by asingle optical fibre with the diameter of a strand of hair.

• Glass in optical fibres is more corrosion resistant than copper cables.

• Due to the nature of optical fibres and total internal reflection,optical fibres are totally secure as they cannot be tapped.Copper cables are less secure as electrical information can bere–routed through wires and therefore tapped.

• Copper cables and optical fibres costs are roughly the same, howevercopper cables require repeaters to boost signals every 1.5 km.Optical fibres require repeaters every 100 km therefore optical fibresare cheaper overall.

All this means that when you talk on your home telephone, dial up theInternet from home or receive a fax, the last place the information hasbeen before reaching the telephone, computer or fax is a copper wire.There are three main reasons for this.

• Fibre optics is a relatively new technology. Houses and businesseswere already networked to telephone exchanges with copper wiringprior to the invention of optic fibres.

• Most telephones, computer modems and fax machines are only ableto convert analog electrical impulses from wires to a useable form.This means that fax machines, telephones and modems are notcapable of changing light impulses from optical fibres to the required

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type of electrical energy, so a decoder must complete this digital toanalog conversion at a telephone exchange.

• The majority of telephones, fax machines and modems are designedto transmit information as analog electrical impulses through wires.A coder must transform analog electrical impulses to digitalimpulses for transmission through telecommunication networks.

Information can be transmitted and received over short distances quitewell through copper wires. Digital information from optical fibres isdecoded and converted to analog electrical pulse information fortransmission into homes and businesses through copper wires as shownon the following page.

Collect some coloured pencils to complete the following activity using thediagram on the following page.

1 Colour the copper wires that transmit analog electrical impulses red inthe diagram on the following page.

2 Colour the copper wires that transmit digital electrical impulses purple.

3 Colour the optical fibres yellow.

4 Colour the light detector orange.

5 Colour the repeater light blue.

6 Colour the light source light green.

7 Colour the coder dark blue.

8 Colour the decoder dark green.


anal

ogel

ectri

cal im

pulse

copp

erwire

digi

tale

lect

rical

impu

lse

digital light impulse digital light impulse

digitalelectricalimpulse

analogelectrical im

pulse

copper wireco

pper

wire

copperw

ire

optical fibreoptical fibre

coder

light source

repeater

light detector

decoder

Energy transformations through telecommunication lines.

Turn to Exercise 6.2 at the back of this part to outline the advantages ofinformation transfer in optical fibres.


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Australian research in fibre optics

The Appendix contains information on a practising female scientist in thefibre optics field. Use the information in the Appendix to answer thefollowing questions.

1 What is the name of the practising female scientist?

_____________________________________________________

2 What qualifications does she have?

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

3 What is she researching?

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

Answers are not supplied for this activity to encourage you to completethe task.


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Appendix

The following information is accessed from: Spaargaren, S.M.R. WesternAustralian Women in Science. Sue Spaargaren.<http://www.swimwithdragons.com.au/cgi–bin/cgiwrap/dragons/allegro.pl?wis_search.Sue+Spaargaren> (accessed 28 November 2000).

Sue Spaargaren

University of Western Australia, Department of Electrical and ElectronicEngineering.

Age 33

Qualifications Bachelors: B Eng (Hons) Electrical and ElectronicEngineering. Masters: M Sc Microwaves andOptoelectronics. Doctorate: PhD ElectricalEngineering on "Radiation Effects in Silica basedWaveguides" (optical fibre related).

School sciencesubjects

Maths, Physics, Chemistry

Main sciencediscipline

Physics

Place of work University

A typical day at work

My job involves planning, performing and writing up experiments onoptical communications. In this field, lasers are used to send light pulsesalong "optical fibres" (a type of thin glass light 'pipe'). The laser light ispicked up at the far end by an electronic light sensor(‘photodetector’ or electronic 'eye').


This method is used today to send telephone calls across long distancesand to send messages between some computers. It is better to use lightpulses in fibres for these applications (rather than electronic pulses inwires) because light pulses transmit information much faster.

In the future, people also want to use optical fibres to speed upconnections between electronic circuit boards inside very fast 'parallel'computers and inside big switches in telephone exchanges.

My work involves testing a new type of light sensor for theseapplications, which can be set to 'see' different laser colours. The morecolours that it can see, the faster the connection will be (i.e. the morephone calls will be transmitted at once). I use different types ofmicroscopes and light experiments to test how well the electronic eyesare working. I then try to use the results from these experiments to helpthe people I work with, who make the sensors, to improve the design ofthe next batch. So far, we have found that the composition and shape ofthe sensor both affect the number of colours seen.

Sometimes I work on my own and sometimes I work with other peopleworking on the same or similar projects. A typical day involves someplanning, or setting up, or performing of experiments. It also involvessome reading in the library (to keep up with the research being done byother people around the world) and some discussion with other people atuni about future experiments. Looking at the results from previousexperiments and writing about them on a computer is also an importantpart of my work. When the results have been written up, we send themto be published in research journals, so that other people around theworld can see what we have been doing. From time to time I also do abit of teaching on optical communications.

The best aspects of my work

I enjoy the variety of work and the mixture between working on my ownand working with other people (some of whom are very experienced andteach me a lot). I like always learning new things from other researchersand the excitement of occasionally getting new results that no–one in theworld has ever got before (after months of hard work on difficultexperiments). Then there is the flexibility of research work which meansthat although you work mainly office hours, sometimes you are extrabusy and have to work in the evenings or at weekends, whereassometimes you are less busy and can leave work early. When I teach Ienjoy meeting students and explaining to them how lasers, optical fibresand light sensors work.

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Personal qualities required for my job

For my job you need to be a curious person who enjoys trying tounderstand how things work. You also need to like doing detailed workand be quite a patient person, as often it takes quite a long time betweenstarting a new experiment and getting good results. You also need to begood at organising your own time when you are working alone, but likeworking with other people as well sometimes.

How I got to be doing the job I am doing

Since both of my parents were scientists, we were always havinginteresting discussions about science at home when I was growing up inthe UK. I enjoyed studying science and maths at school, so I decided tospecialise in these subjects in my last two years at high school.My parents then encouraged me to go to university to help me get a goodjob later. I decided I wanted to study a subject at university which usesmaths and science to solve practical problems–engineering. I chose tostudy electrical and electronic engineering because I felt it was the mostexciting and rapidly changing of the engineering subjects and alsobecause I knew I would learn quite a lot of computing skills, which Ithought I would enjoy and would be very useful for getting a job later on.

Just before the last year of my Bachelors degree, I spent a summer inFrance writing computer programs to help researchers there understandthe results from their optical fibre experiments and became fascinated bythis field. In the end, I decided to study this area further, so I continuedat uni after my Bachelors degree with a Masters degree. After this, Idecided I really wanted to do some full–time research and so I carried onfor several more years to do a PhD on a particular aspect of opticalcommunications.

About a year ago and a half ago I moved to Western Australia fromthe UK. Then I took a holiday for a few months and after that, about ayear ago, I was offered the job I am doing now at the University ofWestern Australia.

Role models

As with a lot of daughters, my father was probably the most influentialperson in my life. He was an electronic engineer and encouraged me(and my brother) to discuss scientific ideas (like how the planets orbit thesun) at home after tea when we were young. Later he encouraged me inmy studies even when I was finding it difficult and was always interestedto know what I was doing.


My mother also encouraged me as she is a biologist and is quite unusualfor her generation because she also studied science at university. She is agreat role model as she is proof that women can be both successful inscience and have a good home life too.

I also had some very good science and physics teachers at school.Particularly my physics teacher, Mr Miller, in the last two years ofschool, who made us work really hard, but told us we could all get topmarks if we tried hard enough. He was very good at explaining the logicbehind physics questions and made the lessons really interesting.

Work ambitions

My work ambitions at the moment are to get as many good results andpublish as many papers as I can and do a good job of teaching, while Igain more research experience. After a few more years experience,I would like to either become a lecturer at university or work in industryas a manager of a research team.

My other interests outside work

I like swimming, snorkelling, aerobics and singing for fun and haverecently started scuba diving, mainly off Rottnest. My husband and Ialso enjoy travelling around the state to explore new places. We reallylike visiting the Margaret River area and have also explored Albany,Augusta and Karinjini National Park (near Port Hedland), as well asGeraldton, Kalbarri and the Abrohlos Islands (near Geraldton).

Being female and working in science

Being female in science has never been a problem for me and issometimes a positive advantage. For example, anything that makesyou different means that people tend to remember you better, so it can beuseful in making a stronger impression when meeting people for thefirst time.

I have recently had a baby daughter and have had no problems inreturning to work part time while she is young. She stays at a day carecentre at the university so I am able to visit her during the day to feed herand give her a cuddle!

In the past women who became scientists and engineers were such asmall minority that they had to fit in with men and do things 'their' way,but I think that is changing. Now women are much more comfortableabout taking advantage of any different approaches they may have tosolving problems.

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Suggested answers

Bending light1 You should see light on your finger which is in the stream of water.

2 The light is held completely within the stream of water.

3 This question asks you to create your own theory. The scientificreason is discussed later in this part.

Total internal reflection1a



norm

al

A

B

C

1bless densemediumfor example air


norm

al

A

B C

1cless densemediumfor example air

more densemediumfor exampleglass

norm

al

A

B

C


2 The beam of light from B to C in the first diagram bends away fromthe normal as it moves into a less dense medium.

3 The angle between the line from A to B and the normal is smallerthan the same angles in the other diagrams.

4 The light line from B to C in this diagram is travelling along theedge of the more dense medium. It does not move into the lessdense medium.

5 The line B to C has a different angle to the normal than the lineA to B in this diagram.

6 The angle between the light line from A to B and the normal is largerthan the same angle in the first diagram.

7 The light line from B to C in this diagram is reflected back into themore dense medium (glass).

8 The angle between A to B and the normal is greater than the sameangles in the first two diagrams.

9 The angles between A and B and the normal and B and C and thenormal the same in this diagram.

Optical fibres

air(less dense)

air(less dense)




A A A

C

E

B

D

B

B

C

C D

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4 Light travels through optic fibres by total internal reflection.

5 Different angles of light reflect off optical fibre walls.

So what is an optical fibre?1 A multimode optic fibre has a consistent refractive index inside the

glass core. A graded optic fibre has high refractive index in thecentre with decreasing refractive index material towards the outsideof the fibre.

2 An optic fibre strand is encased in cladding to protect the delicateglass strand used to transmit light.

3 Graded optical fibres overcome the problems of differingtransmission times.

4 Small diameter core optical fibre is more effective in long distancetelecommunication as it only transmits one impulse at a time,preventing spreading of the light pulse, therefore allowing it to travellonger distances without boosting.

5

6

silicone

buffer jacket

optical fibre

strength layer

glass corecladding

polyurethane

Single optical fibre.


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Exercise - Part 6


Exercise 6.1

Summarise the properties (characteristics) of optical fibres usinginformation on pages 10 to 13.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________


Exercise 6.2

Compare the performance of copper cables and optic fibres intelecommunications in the following areas.

Copper cables compared to optic fibres

Carryingcapacity

Cost

Rate ofinformationtransfer

Security

Size

Evaluate the advantages of optic fibres over copper cables.

_________________________________________________________

_________________________________________________________

_________________________________________________________

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Exercise 6.3

Multiple choice: circle the letter of the most correct answer

1 Information systems can be classified as:

(A) verbal or non–verbal

(B) short or long distance

(C) electronic or non–electronic

(D) all of the above.

2

Earth

Which property of electromagnetic waves does the diagram show?

(A) Electromagnetic waves can be reflected.

(B) Electromagnetic waves travel at the speed of light.

(C) Electromagnetic waves travel through the ionosphere.

(D) Electromagnetic waves may be amplified.

3 Which communication technology does not use energies from theelectromagnetic spectrum to transfer information long distances?

(A) Television.

(B) Radio.

(C) CD played on a sound system.

(D) Mobile telephone.

4

Identify the above wave.

(A) FM wave

(B) AM wave

(C) Sound wave

(D) None of the above


5 Satellites in low Earth orbits are:

(A) mainly used for mobile communications on Earth

(B) travelling faster than satellites in outer orbits

(C) closer to Earth than geostationary satellites


6 The part of the electromagnetic spectrum used for mobile telephonecommunication is:

(A) visible light

(B) X–rays

(C) radio waves

(D) microwaves.

7 The type of energy required to run every modern informationtransfer technology is:

(A) sound energy

(B) electrical energy

(C) kinetic energy

(D) electromagnetic energy.

8 Which electromagnetic waves are most prone to static interference?

(A) FM waves

(B) AM waves

(C) Microwaves

(D) Light waves.

9 Information sent through long distance telephone lines must be:

(A) coded

(B) digitised

(C) decoded


Short answer questions

10 a) Some information systems have similar patterns of informationtransfer. Outline one similarity in the information transferpatterns of televisions and radios.

__________________________________________________

__________________________________________________

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b) Outline one similarity in the information transfer patterns ofcomputer based communications and land connected telephones.

_________________________________________________

_________________________________________________

11 a) Identify two advantages of using a range of information systems.

_________________________________________________

_________________________________________________

b) Identify one advantage of microwave communication over AMand FM radio wave communication.

_________________________________________________

_________________________________________________

12 Choose one information system and outline the energytransformations that occur from the beginning of informationtransmission to the end.

_____________________________________________________

_____________________________________________________

13 Explain how a fax machine works.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

Long answer questions

14 a) Identify what total internal reflection has to do with optic fibres.

_________________________________________________

_________________________________________________

b) Summarise two properties of optic fibres that make them usefulas communication carriers.

_________________________________________________

_________________________________________________


c) Assess why optic fibres are used in preference to copper cablesin telecommunications.

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

15 a) Describe the main features of a geostationary satellite.

__________________________________________________

__________________________________________________

b) Explain why a geostationary satellite must be at a height abovethe Earth where its revolutionary period is the same as that ofthe Earth’s rotation.

__________________________________________________

__________________________________________________

__________________________________________________

c) Justify why a satellite dish on Earth must remain in the sameplace and face the same direction once calibrated to a particularsatellite.

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

16 a) Explain how information can be transmitted betweeninformation systems that aren’t physically linked.

__________________________________________________

b) Critically evaluate a first hand investigation that you did whichcompared communication using AM and FM radio waves. Besure to include your results and conclusion.

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

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Bibliography

Brain, M. Marshall Brain’s How Stuff Works. How a Cell PhoneWorks. <http://www.howstuffworks.com/cell–phone.htm> (accessed 7September 2000)

Brain, M. Marshall Brain’s How Stuff Works. How Compact DisksWork. <http://www.howstuffworks.com/cd.htm> (accessed 7 September2000)

Brain, M. Marshall Brain’s How Stuff Works. How HDTV Works.<http://www.howstuffworks.com/hdtv.htm> (accessed 7 September2000)

Brain, M. Marshall Brain’s How Stuff Works. How Tape RecordersWork. <http://www.howstuffworks.com/cassette.htm> (accessed 26September 2000)

Brain, M. Marshall Brain’s How Stuff Works. How Telephones Work.<http://www.howstuffworks.com/telephone.htm> (accessed 7 September2000)

Brain, M. Marshall Brain’s How Stuff Works. How Television Work.<http://www.howstuffworks.com/tv.htm> (accessed 7 September 2000)

CyberScience. Fibre Optics in the Kitchen.<http://www.publish.csiro.au/cyberScience/helix/TH48/TH48B.htm>(accessed 26 September 2000)

EAN Australia. The system.<http://www.ean.com.au/syst_numb_ret.htm> (accessed 10 October2000)

Encarta Encyclopedia. Facsimile transmission.

Schoenherr, S. History of Radio.<http://history.acusd.edu/gen/recording/television1.html> (accessed 27September 2000)


Schoenherr, S. History of Television.<http://history.acusd.edu/gen/recording/television1.html> (accessed 27September 2000)

Selinsky, D. & Brown, G. Marshall Brain’s How Stuff Works. HowCredit Cards Work. <http://www.howstuffworks.com/credit–card2.htm>(accessed 8 September 2000).

Selinsky, D. & Brown, G. Marshall Brain’s How Stuff Works. HowCredit Cards Work. <http://www.howstuffworks.com/credit–card3.htm>(accessed 8 September 2000).

Spaargaren, S. Western Australian Women in Science. Sue Spaargaren.<http://www.swimwithdragons.com.au/cgi–bin/cgiwrap/dragons/allegro.pl?wis_search.Sue+Spaargaren> (accessed 28 November 2000).

SSCHSC43170 Information Systems

Student evaluation

Name: ________________________ Location: ______________________

We need your input! Can you please complete this short evaluation toprovide us with information about this module. This information willhelp us to improve the design of these materials for future publications.

1 Did you find the information in the module clear and easy tounderstand?

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2 What did you most like learning about? Why?

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3 Which sort of learning activity did you enjoy the most? Why?

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4 Did you complete the module within 30 hours? (Please indicate theapproximate length of time spent on the module.)

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5 Do you have access to the appropriate resources? eg. a computer,the internet, scientific equipment, chemicals, people that can provideinformation and help with understanding science

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Please return this information to your teacher, who will pass it along tothe materials developers at OTEN–DE.

Learning Materials ProductionOpen Training and Education Network – Distance Education

NSW Department of Education and Training

Documents

NNOOTTEE CCAARREEFFUULLLLYY - Millennium Information.pdf · NNOOTTEE CCAARREEFFUULLLLYY The following document was developed by Learning Materials Production, OTEN, DET. Adaptation